设n为正整数,且X的2n次方=5,求(2乘X的3n次方)-3(X²的2n次方)的值.
问题描述:
设n为正整数,且X的2n次方=5,求(2乘X的3n次方)-3(X²的2n次方)的值.
答
x的2n次方=3,
则(x的3n次方)2次方-4(x的3次方)2n次方=(x的2n次方)3次方-4(x的2n次方)3次方=-3(x的2n次方)3次方=-3*(3的3次方)=-81
答
X的2n次方=5
(x^n)^2=5
x^n=√5
(2乘X的3n次方)-3(X²的2n次方)
=2*(x^n)^3-3*(x^n)^4
=2*(√5)^3-3*(√5)^4
=10√5-75