令x-2=y²x=y²+22x=2y²+5x²=y⁴+4y²+4f(y²)=y⁴+4y²+4-2y²-5-3=y⁴+2y²-4所以f(x²)=x⁴+2x²-4求的是f（x+2）打错了令x-2=y+2
x=y+4
2x=2y+8
x²=y²+8y+16
f(y+2)=y²+8y+16-2y-8-3
=y²+6y+5
所以f(x+2)=x²+6x+5