6.
某公司为确定下一年度投入某种产品的宣传费,需了解年宣传费\(x(\)单位:千元\()\)对年销售量\(y(\)单位:\(t)\)和年利润\(z(\)单位:千元\()\)的影响,对近\(8\)年的宣传费\(x_{i}\)和年销售量\(y_{i}(i=1,2,…,8)\)数据作了初步处理,得到的散点图及一些统计量的值.
\(\overline{x}\) | \(\overline{y}\) | \(\overline{w}\) | \({{\sum\limits_{i=1}^{8}{({{x}_{i}}-\overline{x})}}^{2}}\) | \({{\sum\limits_{i=1}^{8}{({{w}_{i}}-\overline{w})}}^{2}}\) | \(\sum\limits_{i=1}^{8}{({{x}_{i}}-\overline{x})}({{y}_{i}}-\overline{y})\) | \(\sum\limits_{i=1}^{8}{({{w}_{i}}-\overline{w})}({{y}_{i}}-\overline{y})\) |
\(46.6\) | \(563\) | \(6.8\) | \(289.8\) | \(1.6\) | \(1469\) | \(108.8\) |
表中\({{w}_{i}}=\sqrt{{{x}_{i}}}\),\(\overline{w}=\dfrac{1}{8}\sum\limits_{i=1}^{8}{{{w}_{i}}}\)
\((1)\)根据散点图,函数\(y=c+d\sqrt{x}\)适宜作为年销售量\(y\)关于年宣传费\(x\)的回归方程,求\(y\)关于\(x\)的回归方程;
\((2)\)已知这种产品的年利润\(x\)与\(x\),\(y\)的关系为\(z=0.2y-x.\)根据\((1)\)的结果回答下列问题:
\(①\)年宣传费\(x=49\)时,年销售量及年利润的预报值是多少\(?\)
\(②\)年宣传费\(x\)为何值时,年利润的预报值最大\(?\)
附:对于一组数据\((v_{1},v_{1})\),\((v_{2},v_{2})\),\(…\),\((v_{n},v_{n})\),其回归直线\(v=α+βv\)的斜率和截距的最小二乘估计分别为\(\widehat{\beta }=\dfrac{\sum\limits_{i=1}^{n}{({{v}_{i}}-\overline{v})({{v}_{i}}-\overline{v})}}{{{\sum\limits_{i=1}^{n}{({{v}_{i}}-\overline{v})}}^{2}}}\),\(\widehat{\alpha }=\overline{v}-\widehat{\beta }\overline{v}\)