solutions to the above equation is :
x1 = -1 + 2.5356i
x2 = -1 + 2.5356 i
In other words these give you no solutions,
Try to solve this quadratic equation:
x^2+2x+(9-7pi/2)=0 // cos((7 * pi) / 2) = 0
and remember that for the quadratic equation to give you real values:
(2n+1)pi/2 > 9 // solve for what values of n you get real values....