Question

f[f(x)]=X4(次方)-6X2(次方)+6则f(X)为多少

Answer 1

f[f(x)]=X^4-6X^2 +6=x^4-6x^2+9-3=(x^2-3)^2 -3 f(x)=x^2 -3 或设f(x)=x^2+b f(f(x))=(x^2+b)^2+b=x^4+2bx^2+b^2+b=x^4-6x^2+6 2b=-6 b=-3 b^2+b=9-3=6 f(x)=x^2-3