5.
探究函数\(f(x){=}2x{+}\dfrac{8}{x}{,}x{∈}(0{,} + \infty)\)的最小值,并确定取得最小值时\(x\)的值\(.\)列表如下:
\(x\) | \(…\) | \(0.5\) | \(1\) | \(1.5\) | \(1.7\) | \(1.9\) | \(2\) | \(2.1\) | \(2.2\) | \(2.3\) | \(3\) | \(4\) | \(5\) | \(7\) | \(…\) |
\(y\) | \(…\) | \(16\) | \(10\) | \(8.34\) | \(8.1\) | \(8.01\) | \(8\) | \(8.01\) | \(8.04\) | \(8.08\) | \(8.6\) | \(10\) | \(11.6\) | \(15.14\) | \(…\) |
请观察表中\(y\)值随\(x\)值变化的特点,完成以下的问题.
\((1)\)函数\(f(x){=}2x{+}\dfrac{8}{x}(x{ > }0)\)在区间\((0,2)\)上递减;函数\(f(x){=}2x{+}\dfrac{8}{x}(x{ > }0)\)在区间 ______上递增\(.\)当\(x= \)______时,\(y_{最小}= \)______.
\((2)\)证明:函数\(f(x){=}2x{+}\dfrac{8}{x}(x{ > }0)\)在区间\((0,2)\)递减.
\((3)\)思考:函数\(y=2x+\dfrac{8}{x}(x > 0)\)时,有最值吗?是最大值还是最小值?此时\(x\)为何值?\((\)直接回答结果,不需证明\()\)