X^2+Y^2=1设x=sint,y=costx+2y=sint+2cost因为√(1^2+2^2)=√5原式=√5(sint*√5/5+cost*2√5/5)令√5/5=cosA,则有sinA=√(1-cos^A)=2√5/5所以原式=√5(sintcosA+costsinA)=√5sin(t+A)所以最大值是√5...