值域[-2,2] f(兀/4+a)= (3√2＋4√2)/5要过程过程：f(x)=根号2(sinx-cosx)f(x)=2(√2/2sinx-√2/2cosx)=2sin(x-兀/4)..x取任何数...所以sin的值域是[-1,1]...所以就是[-2,2]f(a)=2sin(a-兀/4)=6/5cos(a-兀/4)=4/5f(兀/4+a)= 2sin(兀/4+a-兀/4)=2sina=2sin(a-兀/4)cos兀/4+2cos(a-兀/4)sin兀/4= (3√2＋4√2)/5