Question

已知2的x次方+2的-x次方=a（a为常数），求4的x次方+4的-x次方的值

Answer 1

(2的x次方+2的-x次方)^2
=4的x次方+2+4的-x次方
=a^2
所以：4的x次方+4的-x次方=a^2-2

Answer 2

4^x+4^(-x)
=(2^x)²+2+[2^(-x)]²-2
=[2^x+2^(-x)]²-2
=a²-2