The derivative \u0026 tangent line equations

(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

Math: How to Find the Tangent Line of a Function in a Point