Edexcel GCSE (9–1) Mathematics Higher, Chapter 19 · exam-style questions with mark schemes · direct and inverse proportion (y ∝ x², y ∝ √x, y ∝ 1/x², finding k, formulae, percentage changes), proportion graphs, exponential functions y = abx, gradients of tangents and areas under curves (rates, speed, acceleration, distance), translating and reflecting graphs: y = f(x + a), y = f(x) + a, y = −f(x), y = f(−x)