题目 已知 $\omega>0$，函数 $f(x)=\sin\left(\omega x+\dfrac{\mathrm{\pi}}{4}\right)$ 在 $\left(\dfrac{\mathrm{\pi}}{2},\mathrm{\pi}\right)$ 上单调递减，则 $\omega$ 的取值范围是<nn> </nn>． 答案 $\left[\dfrac 12,\dfrac 54\right]$ 解析 如图．<img src="http://bison.img.eduzhixin.com/math-img/190ebe86e6623ada937896c92c99ea95.png" class="img-responsive" /> 备注 每日一题[242]图象的伸缩的练习．