(√a)^2+(√b)^2=1
设sinx=√a,cosx=√b
√a+√b=sinx+cosx=√2sin(x+π/4)
因-1≤sin(x+π/4)≤1
-√2≤√2sin(x+π/4)≤√2
所以)√a+√b≤√2