Find the equation of the tangent to the graph of the function y = f (x) at the point x0; a) f (x) = cosx, x0 = 0.

General view of the tangent equation: y = f ‘(x0) * (x-x0) + f (x0).
f (x) = cosx, x0 = 0.
1) Find the derivative of a given function.
f ‘(x) = (cosx)’ = – sinx.
2) Find the value of the derivative at a given point x0.
f ‘(x0) = f’ (0) = – sin0 = 0.
3) Find the value of the function at a given point x0.
f (x0) = f (0) = cos0 = 1.
3) Substitute all the values in the general view of the tangent.
y = f ‘(x0) * (x-x0) + f (x0) = 0 * (x-0) + 1 = 1.
y = 1 is the equation of the tangent to the graph of the function y = cosx at the point x0.