y=√(a+1)+√(b+1) 则y>0 所以y²=a+1+2√(a+1)(b+1)+b+1 =a+b+2+2√(ab+a+b+1) a+b=1 y²=3+2√(ab+2) 1=a+b>=2√ab √ab<=1/2 ab<=1/4 y²=3+2√(ab+2)<=3+2√(1/4+2)=6 y<=√6 所以最大=√6
