f(x+1)=a(x+1)²+b(x+1)=ax²+bx+x+1x(2a+b)+(a+b)=x(b+1) +12a+b=b+1a+b=1a=b=1/2f(x)的表达式:y=x²/2 + x/2g(x)=2(x²/2 -x/2) +x=x²f[g(x)]=f(x²)=(x²)²/2 + x²/2