Question

已知x,y,a,b∈R,且a/x+b/y=1,求x+y的最小值

Answer 1

a/x+b/y=(√(a/x))^2+(√(b/y))^2=1

两边同乘（√x）^2+(√y)^2

[(√(a/x))^2+(√(b/y))^2]*[（√x）^2+(√y)^2]=x+y

≥(√a+√b)^2