Mathematics

Chapter 1 of the Class 11 Maths NCERT textbook, "Sets", introduces the well-defined collection of objects that underpins all of modern mathematics. Georg Cantor developed set theory in the 1870s while studying trigonometric series.

• 1A set is a well-defined collection of objects; membership is always decidable
• 2Two representation methods: roster form {1,2,3} and set-builder form {x: condition}
• 3Empty set (φ) contains no elements; finite sets have definite cardinality; infinite sets have unlimited elements
• 4A subset (A ⊂ B) means every element of A is also in B; proper subsets exclude equality
• 5Set operations include union (∪), intersection (∩), difference (-), and complement ('); follow commutativity, associativity, and distributivity laws

Chapter 2 of the Class 11 Maths NCERT textbook, "Relations and Functions", covers ordered pairs, cartesian products, relations (domain, range, codomain), and special function types. The chapter PDF is free to download.

• 1Cartesian product P × Q = {(p,q) : p ∈ P, q ∈ Q}; equals empty set if either set is empty
• 2Ordered pairs are equal only if both corresponding elements match: (a,b) = (x,y) iff a=x and b=y
• 3Relation R from set A to B is a subset of A × B; domain = first elements, range = second elements, codomain = entire set B
• 4Function f: A → B requires every element of A to have exactly one image in B; not all relations are functions
• 5Real function has domain and range as R or subsets of R; common types include polynomial, rational, modulus, and signum functions

Chapter 3 of the Class 11 Maths NCERT textbook, "Trigonometric Functions", extends trigonometric ratios to all real angles using radian and degree measures, defining six functions from unit-circle coordinates with applications in physics, engineering, navigation, and seismology.

• 1Angle measurement: degree (1/360 revolution) and radian (arc length / radius in unit circle) related by π rad = 180°
• 2Trigonometric functions defined via unit circle: cos x = x-coordinate, sin x = y-coordinate, with fundamental identity sin²x + cos²x = 1
• 3Domain and range: sin/cos defined for all reals with range [−1, 1]; tan/cot defined except at odd multiples of π/2 and multiples of π respectively
• 4Addition formulas: cos(x+y) = cos x cos y − sin x sin y; sin(x+y) = sin x cos y + cos x sin y; tan(x+y) = (tan x + tan y)/(1 − tan x tan y)
• 5Double-angle formulas: sin 2x = 2 sin x cos x; cos 2x = cos²x − sin²x = 2cos²x − 1 = 1 − 2sin²x; tan 2x = 2tan x/(1 − tan²x)

Chapter 4 of the Class 11 Maths NCERT textbook, "Complex Numbers and Quadratic Equations", extends the real number system to solve equations like x² = -1 by introducing the imaginary unit i, covering complex-number algebra, modulus, conjugate, and the Argand plane.

• 1Complex number z = a + ib has real part a and imaginary part b; two complex numbers are equal only when both parts match
• 2Four basic operations: z₁+z₂=(a+c)+i(b+d), z₁z₂=(ac-bd)+i(ad+bc), division via multiplicative inverse z⁻¹=z̄/|z|²
• 3Powers of imaginary unit i repeat in cycles of 4: i²=-1, i³=-i, i⁴=1, then repeats; i⁻¹=-i, i⁻²=-1, i⁻³=i, i⁻⁴=1
• 4Square roots of negative numbers: √(-a)=√(a)i for positive a; but √(ab)≠√a·√b when both a,b<0 (contradiction to i²=-1)
• 5Modulus |z|=√(a²+b²) measures distance from origin; conjugate z̄=a-ib is mirror image across real axis in Argand plane

Chapter 5 of the Class 11 Maths NCERT textbook, "Linear Inequalities", covers statements relating real numbers or algebraic expressions using <, >, ≤, or ≥, teaching how to solve one-variable and two-variable linear inequalities algebraically and graphically.

• 1An inequality consists of two real numbers or algebraic expressions related by <, >, ≤, or ≥; unlike equations, inequalities represent ranges of values, not exact solutions.
• 2The solution of an inequality is any value of the variable that makes the statement true; solutions are often represented as intervals (e.g., x ∈ (−∞, 2)) or graphically on a number line.
• 3Rule 1: Equal numbers may be added to or subtracted from both sides of an inequality without changing the inequality sign; Rule 2: Multiplying or dividing both sides by a positive number preserves the sign, but by a negative number reverses it (e.g., 3 > 2 becomes −3 < −2).
• 4Linear inequalities in one variable have the form ax + b < 0 (or >, ≤, ≥); in two variables, ax + by < c (or >, ≤, ≥); higher-degree inequalities like ax² + bx + c ≤ 0 are quadratic, not linear.
• 5Double inequalities (e.g., −8 ≤ 5x − 3 < 7) are solved by treating them as two simultaneous inequalities; graphically, the solution is the region where both conditions overlap on the number line.

Chapter 6 of the Class 11 Maths NCERT textbook, "Permutations and Combinations", covers counting techniques, factorial notation, and formulas for arranging and selecting objects without listing them explicitly.

• 1Fundamental Principle of Counting: If an event can occur in m ways and another in n ways, the total combined occurrences = m × n
• 2Factorial notation: n! = n × (n-1) × (n-2) × ... × 1, with 0! = 1 by definition
• 3Permutations (nPr) count ordered arrangements; formula: nPr = n!/(n-r)! for 0 ≤ r ≤ n
• 4Combinations (nCr) count unordered selections; formula: nCr = n!/[r!(n-r)!]; satisfies nCn-r = nCr
• 5Permutations with repetition allowed: nr (each of r positions can be filled r ways)

Chapter 7 of the Class 11 Maths NCERT textbook, "Binomial Theorem", provides a formula to expand (a + b)ⁿ for any positive integer n without repeated multiplication, using binomial coefficients ⁿCᵣ from the terms ⁿC₀aⁿ + ⁿC₁aⁿ⁻¹b + … + ⁿCₙbⁿ.

• 1Binomial Theorem: (a + b)ⁿ = ΣⁿCₖaⁿ⁻ᵏbᵏ from k=0 to n, where ⁿCᵣ = n!/(r!(n–r)!)
• 2Pascal's triangle and binomial coefficients provide expansion coefficients without multiplication
• 3There are always (n+1) terms in (a + b)ⁿ expansion, with indices of a and b summing to n in each term
• 4Special cases: (x – y)ⁿ uses alternating signs; (1 + x)ⁿ simplifies to ⁿC₀ + ⁿC₁x + ⁿC₂x² + ...
• 5Practical applications include computing large powers (e.g., (98)⁵ = 9039207968) and proving divisibility (e.g., 6ⁿ – 5ⁿ ≡ 1 mod 25)

Chapter 8 of the Class 11 Maths NCERT textbook, "Sequences and Series", covers arithmetic and geometric progressions, their formulas for nth terms and sums, geometric means, and the relationship between arithmetic and geometric means.

• 1A sequence is an ordered collection of numbers with an identified position for each term; finite sequences have fixed terms, infinite sequences never end
• 2Geometric progression (G.P.) is defined when the ratio of any term to its preceding term is constant (r), written as a, ar, ar², ar³, ...
• 3The nth term of a G.P. is an = ar^(n–1); sum of first n terms is Sn = a(rn–1)/(r–1) when r ≠ 1, or Sn = na when r = 1
• 4Geometric mean (G.M.) of two positive numbers a and b is √(ab), and any two positive numbers can have multiple geometric means inserted between them
• 5Relationship between arithmetic mean (A.M.) and geometric mean: A ≥ G, with equality only when a = b

Chapter 9 of the Class 11 Maths NCERT textbook, "Straight Lines", treats lines as coordinate-geometry figures defined through slope-intercept, point-slope, or intercept forms, enabling analysis of parallelism, perpendicularity, and distance.

• 1Slope m = tan θ measures line inclination; undefined for vertical lines (θ = 90°)
• 2Slope from two points: m = (y₂ - y₁)/(x₂ - x₁) works for acute and obtuse angles
• 3Parallel lines have equal slopes; perpendicular lines have slopes satisfying m₁m₂ = -1
• 4Equation forms: point-slope y - y₀ = m(x - x₀), two-point, slope-intercept y = mx + c, intercept x/a + y/b = 1
• 5Perpendicular distance from point (x₁,y₁) to line Ax + By + C = 0: d = |Ax₁ + By₁ + C|/√(A² + B²)

Chapter 10 of the Class 11 Maths NCERT textbook, "Conic Sections", covers curves formed by intersecting a right circular cone with a plane — circles, ellipses, parabolas, and hyperbolas — each with distinct geometric properties and equations used in planetary motion and reflector design.

• 1A circle: (x – h)² + (y – k)² = r², where (h, k) is the center and r is the radius
• 2A parabola: y² = 4ax (opening rightward), where the focus is at (a, 0) and directrix is x = –a; latus rectum length = 4a
• 3An ellipse: x²/a² + y²/b² = 1 (foci on x-axis), where c² = a² – b² and eccentricity e = c/a; latus rectum length = 2b²/a
• 4A hyperbola: x²/a² – y²/b² = 1 (transverse axis on x-axis), where c² = a² + b² and eccentricity e = c/a (always > 1); latus rectum length = 2b²/a
• 5Degenerate cases occur when the plane cuts through the cone's vertex: a point (α < β ≤ 90°), a straight line (β = α), or pair of intersecting lines (0 ≤ β < α)

Chapter 11 of the Class 11 Maths NCERT textbook, "Introduction to Three Dimensional Geometry", introduces the 3D coordinate system of three mutually perpendicular axes and planes, representing a point in space by an ordered triplet (x, y, z) and covering distances and octants.

• 1Three-dimensional space uses three mutually perpendicular coordinate axes (x, y, z) that meet at the origin O
• 2The three coordinate planes (XY, YZ, ZX) divide space into eight octants, each with distinct sign patterns for coordinates
• 3A point P(x, y, z) has coordinates representing perpendicular distances from the YZ, ZX, and XY planes respectively
• 4Distance between two points is calculated using PQ = √[(x₂−x₁)² + (y₂−y₁)² + (z₂−z₁)²]; distance from origin to Q(x, y, z) is √(x² + y² + z²)
• 5Points lying on axes have two zero coordinates; points in coordinate planes have one zero coordinate

Chapter 12 of the Class 11 Maths NCERT textbook, "Limits and Derivatives", is an introduction to calculus covering how functions change; derivatives measure the instantaneous rate of change at a point, computed as the limit of average rates of change.

• 1Limit of f(x) as x→a equals l when both left and right hand limits exist and equal l (denoted lim f(x) = l)
• 2Derivative f'(a) = lim[f(a+h)−f(a)]/h measures the slope of the tangent to the curve at point a
• 3Algebra of limits: sums, differences, products, and quotients of limits equal limits of those operations (when denominators ≠ 0)
• 4Key trigonometric limits: lim(sin x/x) = 1 and lim(1−cos x)/x = 0 as x→0; proven using the sandwich theorem
• 5Derivative rules: (u+v)' = u'+v', (uv)' = u'v+uv' (product rule), (u/v)' = (u'v−uv')/v² (quotient rule)

Chapter 13 of the Class 11 Maths NCERT textbook, "Statistics", covers measures of central tendency (mean, median, mode) and measures of dispersion (range, mean deviation, variance, standard deviation) for grouped and ungrouped data, analysing how data varies from a central value.

• 1Measures of central tendency alone are insufficient; dispersion measures reveal data scatter and variability
• 2Range is the simplest dispersion measure: difference between maximum and minimum values
• 3Mean deviation measures average absolute deviation from mean or median; cannot be algebraically manipulated
• 4Variance is the mean of squared deviations from the mean; standard deviation is its positive square root
• 5Step-deviation method simplifies calculations when data values or class midpoints are large

Chapter 14 of the Class 11 Maths NCERT textbook, "Probability", quantifies the chances of events through axiomatic rules: for any event E, 0 ≤ P(E) ≤ 1, with P(S) = 1 for the sample space and P(φ) = 0 for the impossible event.

• 1An event is any subset of a sample space; simple events contain one sample point, compound events contain multiple sample points
• 2Mutually exclusive events cannot occur together (A ∩ B = φ); exhaustive events cover the entire sample space when combined
• 3The three axioms of probability: P(E) ≥ 0, P(S) = 1, and P(E ∪ F) = P(E) + P(F) for mutually exclusive events
• 4For equally likely outcomes, probability of event A equals the ratio n(A)/n(S) of favorable to total outcomes
• 5The union rule: P(A ∪ B) = P(A) + P(B) - P(A ∩ B); complement rule: P(A') = 1 - P(A)

Appendix A.1 of the Class 11 Maths NCERT textbook covers four special infinite series — the Binomial Series for any real index m, the Infinite Geometric Series, the Exponential Series defining the number e, and the Logarithmic Series — with their expansions, convergence conditions, and worked examples.

• 1An infinite series is the indicated sum a1 + a2 + a3 + ... of an infinite sequence, expressible in sigma notation as ∑ak from k = 1 to ∞.
• 2The Binomial Theorem for any index states (1+x)^m = 1 + mx + m(m–1)x²/1·2 + m(m–1)(m–2)x³/1·2·3 + ..., valid when |x| < 1, where m may be a negative integer or a fraction.
• 3For the expansion of (a+b)^m, the series is valid when |b| < |a|; the general term is m(m–1)(m–2)···(m–r+1) · a^(m–r) · b^r / (1·2·3···r).
• 4The Infinite Geometric Series a + ar + ar² + ... converges to S = a/(1–r) whenever |r| < 1; when |r| ≥ 1 the series does not have a finite sum.
• 5The number e — introduced by Leonhard Euler in his calculus text in 1748 — is defined as the sum of the series 1 + 1/1! + 1/2! + 1/3! + ..., and satisfies 2 < e < 3.

Appendix A.2 of the Class 11 Maths NCERT textbook covers mathematical modelling — translating a real-life problem into mathematical form through the stages of formulation, solution, and interpretation/validation — so situations too complex to measure directly can be studied mathematically.

• 1Mathematical modelling is defined as an attempt to study some part of a real-life problem in mathematical terms by converting a physical situation into mathematics under suitable conditions.
• 2The process follows four stages: (1) understanding the problem, (2) formulation — which itself has two sub-steps: identifying relevant factors/parameters and writing a mathematical description such as an equation or inequality, (3) finding the solution, and (4) interpretation/validation.
• 3Validation measures model effectiveness by comparing results from the mathematical model with known real-world facts; if the model is not accurate enough it is revised, leading to a cyclic modelling process.
• 4Models contain built-in assumptions and approximations; for example, the simple pendulum model neglects the mass of the string and resistance of the medium, which accounts for a small but measurable error between calculated and observed periods.
• 5The Konigsberg bridge problem (1736) shows how Euler proved that crossing all seven bridges exactly once is impossible because all four vertices in his network diagram are odd-degree; this work founded graph theory.

Free PDF of official answers for the Class 11 Maths NCERT textbook, covering all exercises across Chapters 1–14 from Sets through Probability — no sign-up required.

• 1Covers all 14 chapters: Sets, Relations and Functions, Trigonometric Functions, Complex Numbers, Linear Inequalities, Permutations and Combinations, Binomial Theorem, Sequences and Series, Straight Lines, Conic Sections, Three Dimensional Geometry, Limits and Derivatives, Statistics, and Probability.
• 2Includes answers to numbered exercises for each chapter — e.g., Exercises 1.1–1.5, 2.1–2.3, 3.1–3.3, 6.1–6.4, 8.1–8.2, 9.1–9.3, 10.1–10.4, 12.1–12.2, 13.1–13.2, and 14.1–14.2.
• 3Every chapter's Miscellaneous Exercise answers are included alongside the main exercises.
• 4Chapters with single main exercises (4, 5, 7, 11) still include their full Miscellaneous Exercise answers.
• 5Answers cover a range of question types: set notation, trigonometric identities, complex number arithmetic, inequality solution sets, permutation/combination counts, binomial expansions, sequence terms and sums, coordinate geometry equations, conic section parameters, 3D distance formulas, limits, derivatives, statistical measures (mean, variance), and probability values.