g(x)=f(2-x²)=8+2（2-x²）-（2-x²）²=-x^4+2x^2+8
令t=x^2
g(x)=-t^2+2t+8(t≥0)
=-(t-1)^2+9
g(x)的单调区间:[01]递增,[1+∞）递减