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Advanced · Level 12 of 12

Calculus, matrices and vectors

The ideas behind engineering, data science and economics: functions, limits, derivatives, integrals, matrices and vectors. Kanakku keeps a picture in front of each idea, such as a curve with its tangent or sets drawn as overlapping circles, so the formulas mean something before you start drilling them.

Relations & functions

Types of relations, one-one and onto functions, composition and inverses.

Key idea

A function is one-one if different inputs give different outputs, and onto if every output in the codomain is reached.

How to do it

  1. Reflexive: aRa for all a. Symmetric: aRb ⇒ bRa. Transitive: aRb and bRc ⇒ aRc.
  2. Equivalence relation: all three.
  3. One-one: no two inputs share an output. Onto: every output is hit.
  4. f∘g means: do g first, then f.
Practise relations & functions

Matrices & determinants

Order, multiplication, transpose, determinants and inverses.

Key idea

A matrix is a grid of numbers. To multiply, go along a row of the first and down a column of the second.

How to do it

  1. Order = rows × columns.
  2. (AB)ᵢⱼ = row i of A · column j of B.
  3. Transpose: rows become columns.
  4. det of a 2×2 = ad − bc. A matrix has an inverse only if det ≠ 0.
Practise matrices & determinants

Continuity & differentiability

Standard derivatives, the chain and product rules, and continuity.

Key idea

A function is continuous if its graph has no breaks. To differentiate combinations, use the chain, product and quotient rules.

How to do it

  1. d/dx sin x = cos x, cos x → −sin x, eˣ → eˣ, log x → 1/x.
  2. Chain rule: outside derivative × inside derivative.
  3. Product rule: (uv)′ = u′v + uv′.
  4. Continuous at a: the left limit, right limit and f(a) are all equal.
Practise continuity & differentiability

Applications of derivatives

Increasing and decreasing, maxima and minima, tangents and rates.

Key idea

Where f′(x) > 0 the function rises; where f′(x) < 0 it falls. Where f′(x) = 0 it may have a maximum or minimum.

How to do it

  1. Increasing where f′(x) > 0, decreasing where f′(x) < 0.
  2. Turning points: solve f′(x) = 0.
  3. f″(x) > 0: minimum. f″(x) < 0: maximum.
  4. Rate of change: dA/dt = dA/dr × dr/dt.
Practise applications of derivatives

Integrals

Integration as reverse differentiation, and as area under a curve.

Key idea

Integration reverses differentiation. A definite integral gives the area under a curve between two x-values.

How to do it

  1. ∫xⁿ dx = xⁿ⁺¹/(n + 1) + C (n ≠ −1).
  2. ∫cos x dx = sin x + C, ∫eˣ dx = eˣ + C, ∫1/x dx = log|x| + C.
  3. Definite integral: F(b) − F(a).
  4. Area under y = f(x) from a to b = ∫ₐᵇ f(x) dx.
Practise integrals

Differential equations

Order and degree, and simple solutions.

Key idea

A differential equation links a function with its derivatives. Solving it means finding the function.

How to do it

  1. Order: the highest derivative in the equation.
  2. Degree: the power of that highest derivative (when the equation is a polynomial in the derivatives).
  3. Variables separable: put all the y on one side and all the x on the other, then integrate.
Practise differential equations

Vectors

Magnitude, the dot product and perpendicular vectors.

Key idea

A vector has size and direction. The dot product measures how much two vectors point the same way; 0 means they are at right angles.

How to do it

  1. |a⃗| = √(a₁² + a₂² + a₃²).
  2. a⃗ · b⃗ = a₁b₁ + a₂b₂ + a₃b₃.
  3. a⃗ · b⃗ = |a⃗||b⃗| cos θ.
  4. Perpendicular ⇔ a⃗ · b⃗ = 0.
Practise vectors

Three-dimensional geometry

Distance, midpoints and direction ratios in 3D.

Key idea

3D geometry adds a z-coordinate. The formulas are the same as in 2D, with one more term.

How to do it

  1. Distance = √((x₂ − x₁)² + (y₂ − y₁)² + (z₂ − z₁)²).
  2. Midpoint: average each coordinate.
  3. Direction ratios of a line through two points: (x₂ − x₁, y₂ − y₁, z₂ − z₁).
Practise three-dimensional geometry

Linear programming

Find the best value of Z at the corners of the feasible region.

Key idea

In linear programming, the maximum or minimum of Z always happens at a corner point of the feasible region.

How to do it

  1. Draw the constraints and shade the feasible region.
  2. List the corner points.
  3. Work out Z at each corner.
  4. The largest is the maximum; the smallest is the minimum.
Practise linear programming

Probability

Conditional probability, independent events and binomial chances.

Key idea

Conditional probability P(A|B) is the chance of A when you already know B happened: P(A ∩ B) ÷ P(B).

How to do it

  1. P(A|B) = P(A ∩ B) ÷ P(B).
  2. Independent events: P(A ∩ B) = P(A) × P(B).
  3. Total probability: add up the chances through each route.
  4. Exactly k successes in n tries (p = ½): ⁿCₖ ÷ 2ⁿ.
Practise probability

Games and tools for level 12