find the value of a^3-1/8a^3 ,if a^2+1/4a^2=10

Answer 1

a^3 - a^3/8.

a^2 + a^2/4 = 10.
Multiply both sides by 4:
4a^2 + a^2 = 40,
5a^2 = 40,
a^2 = 8,
a = +-2*sqrt2.

(2*sqrt2)^3 - (2*sqrt2)^3 / 8,
8(2*sqtr2) - 8(2*sqrt2) / 8,
8(2*sqrt2) - (2*sqrt2),
7(2*sqrt2),
14*sqrt2 = 19.8.