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高中数学必修 第一册(648题)


已知函数 \(f(x) = \sin (2x - \frac{\pi }{6}) + 2{\cos ^2}x - 1\)


若函数 \(y = f(x)\) 在区间\(\left [ {0,m} \right ]\)上的值域为\(\left [ {\frac {1} {2},1} \right ]\),求实数 \(m\) 的取值范围.




知识点:第五章 三角函数


参考答案:\(\because x\in \left [ {0,m} \right ]\),\(2x+\frac {\pi } {6}\in \left [ {\frac {\pi } {6},2m+\frac {\pi } {6}} \right ]\) ,\(f\left ( {x} \right )\in \left [ {\frac {1} {2},1} \right ]\),

\(\therefore \) \(\frac{\pi }{2}⩽2m + \frac{\pi }{6}⩽\frac{{5\pi }}{6}\) ,\(\therefore \) \(\frac{\pi }{6}⩽m⩽\frac{\pi }{3}\) ,

故实数 \(m\) 的取值范围为\(\left [ {\frac {\pi } {6},\frac {\pi } {3}} \right ]\).


解析:



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