0.97 = 850-a^2 / 750
I took your equation to mean: 0.97 =( 850-a^2) / 750 cross multiply 727.50 =850 - a^2 a^2 =850 - 727.50 a^2 = 122.5 a = +or- sqrt(122.5) a=+or- 7sqrt(5/2)