函数y=-cos(x-π/3) ,x∈(2π/3,4π/3)的最大值是函数y=-cos(x-π/3) (x∈[2π/3,4π/3])的最大值是多少 补充一题.已知cos(π+α)=1/2 则sin(π/2-α)的值为
问题描述：
函数y=-cos(x-π/3) ,x∈(2π/3,4π/3)的最大值是
函数y=-cos(x-π/3) (x∈[2π/3,4π/3])的最大值是多少
补充一题.已知cos(π+α)=1/2 则sin(π/2-α)的值为
答
1) x∈[2π/3,4π/3] ==> (x-π/3)∈[π/3,π]
==> 在此区间上余弦函数最大值为 y=cosπ/3=1/2
2) sin(π/2-α)=cosα=-cos(π+α)=-1/2