函数y=3sin(x/3)+4cos(x/3)的最大值.
问题描述：
函数y=3sin(x/3)+4cos(x/3)的最大值.
答
y=3sin(x/3)+4cos(x/3)
=5[3/5sin(x/3)+4/5cos(x/3)]
设cosθ=3/5（0y=5sin(x/3+θ)
则y的最大值为5
答
y=3sin(x/3)+4cos(x/3)
=5[(3/5)sin(x/3)+(4/5)cos(x/3)]
=5sin(x/3 + α ) (其中cosα=3/5,sinα=4/5)
∈[-5,5]