Use a graph to explain how you know whether the tangent

Question

(a) Find the tangent line approximation to cos x at x = π/4.

(b) Use a graph to explain how you know whether the tangent line approximation is an under- or overestimate for 0 ≤ x ≤ π/2.

(c) To one decimal place, estimate the error in the approximation for 0 ≤ x ≤ π/2