Question

f（x-x分之1）=x方+x方分之1 则f（3）=?、

Answer 1

令t=x-1/x,t^2=x^2+1/x^2-2

有x^2+1/x^2=t^2+2

f(t)=t^2+2

所以f(x)=x^2+2

则f(3)=11