已知:x^2n=5,求（1/3x^3n)^2-3*(x^2)^2n的值
问题描述：
已知:x^2n=5,求（1/3x^3n)^2-3*(x^2)^2n的值
答
[(1/3)x^3n]^2-3(x^2)^2n
= (1/9)x^6n-3x^4n
= (1/9)(x^2n)^3-3(x^2n)^2
= (1/9)*5^3-3*5^2
= -550/9