根据导数判断函数增减.

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B∵y′=-cosx,当x∈[-π/2,π/2]时,y′＜0
∴y在区间[-π/2,π/2]上单调递减
======以下答案可供参考======
供参考答案1:
y’=-cosx
令y’=0解得x=π/2+kπ
即y’在【-π/2，π/2】》0
即递减