hi. i have a question which is the thomas calculus at chapter 5 additional exercises. can you help me i could not solve it ;

find f(pi/2) if the area under the curve y=f(x) from x=0 to x=a is ;

((a^2)/2) + (a*sin(a))/2 + (pi*cos(a))/2 ;

how should i think in order to solve this. please help me...