若n为正整数,且x的2n次方=7,求(3x的3n次方)的2次方-13(x的2次方)的2n次的值
问题描述:
若n为正整数,且x的2n次方=7,求(3x的3n次方)的2次方-13(x的2次方)的2n次的值
答
解
x^2n=7
(3x^3n)²-13(x²)^2n
=9x^6n-13x^4n
=9×(2^2n)³-13×(2^2n)²
=(2^2n)²(9×2^2n-13)
=49×(9×7-13)
=49×50
=2450