Let f(x) be a continous function such that its first two derivatives f'(x) and f''(x) are continous. The tangents to the graph of f(x) at the points with abscissa x=a and x=b make with the X-axies angles π / 3 and π /4 respectively. then the value of the integral

Integrate [ f'(x) * f''(x) dx ] from a to b equals?

a. 1-root3

b. 0

c. 1

d. -1

Thanks