w=∫ydx+x^2dy=∫(从0到1) [x^a+a*x^(a+1)]dx=(a^2+2a+2)/[(a+1)(a+2)]=1-1/(a+2/a-3)
根据均值不等式,a+2/a>=2根号下（a*2/a）=2乘以根号2,取等号时a=根号2
综上,a=根号2时做功最小