can anyone please help me with finding the maximum and minimum points for this equation??

(pi)x^2 + 4(pi)^2.x^2 - 28(pi).x.a + 49a

(a=tan72)

the first derivative according to me is... 2(pi)x + 8(pi)^2.x.a-28(pi)a

ive been trying to make x the subject of this equation, when i do get the x, what do i do with it???

somebody please help!!!