What is 8x squared + 7=0 using the quadratic formula

I think you mean 8x^2 + 7 = 0

a = 8 b = 0 c = 7

x = [-b + - square root (b^2 - 4*a*c) ] / 2a

x = [0 + - square root (0 - 4*8*7) ] / 2*8

x = + - square root (-224) / 16

x = + - 14.9666295471 * i / 16

x = + 0.9354143467 i

x = - 0.9354143467 i