f(x+（1/x）)=x^2+1/x^2-3,则f(2x)等于

题目

f(x+（1/x）)=x^2+1/x^2-3,则f(2x)等于

答案

f(x+1/x)=x^2+1/x^2-3
=(x+1/x)^2-5
令:t=x+(1/x)
--> f(t)=t^2-5
再令:t=2x (这时 t是自变量)
f(2x)=4x^2-5