Mathematics — Calculus, Vectors, 3D, Probability & More
1. Relations and Functions
Types of Relations
Reflexive: (a,a)∈R ∀a. Symmetric: (a,b)∈R ⇒ (b,a)∈R. Transitive: (a,b)∈R∧(b,c)∈R ⇒ (a,c)∈R. Equivalence = Reflexive + Symmetric + Transitive.
Functions
- One-One (Injective) : f(x₁)=f(x₂) ⇒ x₁=x₂. Onto (Surjective) : Range = Codomain. Bijective: Both = INVERTIBLE.
- Composition: (f∘g)(x) = f(g(x)). f is invertible ⇔ f is bijective.
2. Inverse Trigonometric Functions
| Function | Domain | Principal Value Range |
|---|---|---|
| sin⁻¹x | [-1, 1] | [-π/2, π/2] |
| cos⁻¹x | [-1, 1] | [0, π] |
| tan⁻¹x | R | (−π/2, π/2) |
Key Identities: sin⁻¹x + cos⁻¹x = π/2. tan⁻¹x + cot⁻¹x = π/2. tan⁻¹x + tan⁻¹y = tan⁻¹[(x+y)/(1−xy)].
3. Matrices and Determinants
Matrix Operations
- Multiplication: AB ≠ BA (generally). (AB)′ = B′A′.
- Inverse: A⁻¹ = adj(A)/|A| (|A| ≠ 0).
Determinants — Properties
- |A′| = |A|. Interchanging rows → sign changes. Identical rows → |A|=0.
- Cramer's Rule: For AX = B, xᵢ = |Aᵢ|/|A|.
4. Continuity and Differentiability
Continuity at x = a
f is continuous if lim(x→a⁻) f(x) = lim(x→a⁺) f(x) = f(a).
Differentiability
f is differentiable if lim(h→0) [f(x+h)−f(x)]/h EXISTS. Differentiability ⇒ Continuity. Converse NOT true (|x| at x=0).
Differentiation Techniques
Chain rule. Logarithmic differentiation. Implicit functions. Parametric forms. Second-order derivatives.
Rolle's Theorem
If f continuous on [a,b], differentiable on (a,b), and f(a)=f(b) → ∃c∈(a,b): f′(c)=0.
Mean Value Theorem (MVT)
∃c∈(a,b): f′(c) = [f(b)−f(a)]/(b−a).
5. Application of Derivatives
Rate of Change. Tangents and Normals.
Increasing/Decreasing: f′(x) > 0 ⇒ increasing. f′(x) < 0 ⇒ decreasing.
Maxima and Minima
- First Derivative Test: Critical points (f′=0). Check sign change.
- Second Derivative Test: f″>0 ⇒ local MINIMUM. f″<0 ⇒ local MAXIMUM.
6. Integrals
Indefinite Integration — Antiderivative + C.
Methods
Substitution. Integration by Parts: ∫u dv = uv − ∫v du. ILATE rule. Partial Fractions.
Definite Integral — ∫ₐᵇ f(x)dx = F(b)−F(a). (FTC)
Properties: ∫ₐᵇ = −∫ᵦᵃ. ∫₋ₐᵃ f(x)dx = 0 (odd) = 2∫₀ᵃ (even).
Area Under Curves
Area between y=f(x) (upper) and y=g(x) (lower) from a to b: ∫ₐᵇ [f(x)−g(x)] dx.
7. Differential Equations
Order and Degree.
Solving First-Order, First-Degree:
- Variable Separable: dy/dx = f(x)g(y) → ∫(1/g)dy = ∫f dx.
- Homogeneous: y=vx substitution → separable.
- Linear: dy/dx + Py = Q. IF = e^∫Pdx. Solution: y·IF = ∫Q·IF dx + C.
8. Vector Algebra
Dot Product: a·b = |a||b|cos θ = a₁b₁+a₂b₂+a₃b₃. a·b=0 ⇔ a⟂b.
Cross Product: a×b = |a||b| sin θ n̂. |a×b| = area of parallelogram. a×b=0 ⇔ a∥b.
Scalar Triple Product: [a b c] = a·(b×c) = volume of parallelepiped. =0 ⇒ coplanar.
9. Three-Dimensional Geometry
Direction Cosines (l,m,n): l²+m²+n²=1.
Line: r = a + λb. (x−x₁)/a = (y−y₁)/b = (z−z₁)/c.
Plane: r·n = d. ax+by+cz+d=0. Intercept form: x/a + y/b + z/c = 1.
Distances and Angles
- Distance of point from plane: |ax₁+by₁+cz₁+d|/√(a²+b²+c²).
- Angle between two planes: cos θ = |n₁·n₂|/(|n₁||n₂|).
10. Linear Programming
Graphical Method
- Graph constraints as lines. Shade FEASIBLE REGION. 2. Find corner points. 3. Evaluate objective function Z at each corner. 4. Optimal value at a corner (if bounded).
11. Probability
Conditional Probability: P(A|B) = P(A∩B)/P(B).
Bayes' Theorem
P(Bᵢ|A) = [P(Bᵢ)·P(A|Bᵢ)] / ΣⱼP(Bⱼ)·P(A|Bⱼ). 'Reverses the conditional — given the EVIDENCE, what's the probability of the CAUSE?'
Random Variables
- Discrete: Probability mass function. P(X=xᵢ) = pᵢ. Σpᵢ = 1.
- Mean μ = Σxᵢpᵢ = E(X). Variance σ² = E(X²) − [E(X)]².
Binomial Distribution
n independent trials. Two outcomes (Success p, Failure q=1−p). P(X=r) = ⁿCᵣ pʳ qⁿ⁻ʳ (r=0,1,...,n). Mean = np. Variance = npq.
