稍等,馬上給你答案y=1/2sin(π/4-2x/3)=-1/2sin(2x/3-π/4)
單減間區(qū)間求法
令2kπ-π/2 =< 2x/3-π/4 <= 2kπ+π/2
解得單減間區(qū)間為[3kπ-3π/8,3kπ+9π/8]]k屬于正整數(shù)
類似單增區(qū)間求法
令2kπ+π/2 =< 2x/3-π/4 <= 2kπ+3π/2
解得單增間區(qū)間為[3kπ+9π/8,3kπ+21π/8]，k屬于正整數(shù)

第二個畫圖就可以解決
sin(x+（π/4）)的單調(diào)增區(qū)間為[2kπ-3π/4 ,2kπ+π/4],加絕對值后單增區(qū)間為
[kπ-π/4 ,kπ+π/4】，加負號后單增區(qū)間為[kπ+π/4 ,kπ+3π/4],

單減區(qū)間同理可得[kπ——π/4 ,kπ+π/4],k屬于正整數(shù)