Question

给出2的n次方加上2的-n次方等于k、4的n加上4的-n次方等于多少

Answer 1

2^n+2^(-n)=k

即2^n+1/2^n=k

两边平方

(2^n+1/2^n)^2=k^2

4^n+2+1/4^n=k^2

所以4^n+4^(-n)=k^2-2