2.
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\(8\)年的年宣传费\({{x}_{i}}\)和年销售量\({{y}_{i}}(i=1,2,…,8)\)数据作了初步处理,得到如右图的散点图及一些统计量的值.
\(\overline{x}\) | \(\overline{y}\) | \(\overline{\omega }\) | \(\sum\limits_{i=1}^{8}{{{\left( {{x}_{i}}-\overline{x} \right)}^{2}}}\) | \(\sum\limits_{i=1}^{8}{{{\left( {{\omega }_{i}}-\overline{\omega } \right)}^{2}}}\) | \(\sum\limits_{i=1}^{8}{\left( {{x}_{i}}-\overline{x} \right)}\left( {{y}_{i}}-\overline{y} \right)\) | \(\sum\limits_{i=1}^{8}{\left( {{\omega }_{i}}-\overline{\omega } \right)}\left( {{y}_{i}}-\overline{y} \right)\) |
\(46.6\) | \(563\) | \(6.8\) | \(289.8\) | \(1.6\) | \(1469\) | \(108.8\) |
表中\({{\omega }_{i}}=\sqrt{{{x}_{i}}}\),\(\overline{\omega }=\dfrac{1}{8}\sum\limits_{i=1}^{8}{{{\omega }_{i}}}\),
\((\)Ⅰ\()\)根据散点图判断,\(y=a+bx\)与\(y=c+d\sqrt{x}\)哪一个适宜作为年销售量\(y\)关于年宣传费\(x\)的回归方程类型?\((\)给出判断即可,不必说明理由\()\)
\((\)Ⅱ\()\)根据\((\)Ⅰ\()\)的判断结果及表中数据,建立\(y\)关于\(x\)的回归方程;
\((III)\)已知这种产品的年利润\(z\)与\(x\),\(y\)的关系为\(z=0.2y-x\),根据\((\)Ⅱ\()\)的结果,回答下列问题:
\(\)年宣传费\(x=49\)时,年销售量及年利润的预报值是多少?
\(\)当年宣传费\(x\)为何值时,年利润的预报值最大?
附:对于一组数据\(\left( {{u}_{1}},{{v}_{1}} \right),\left( {{u}_{2}},{{v}_{2}} \right),\cdots \left( {{u}_{n}},{{v}_{n}} \right)\),其回归直线\(v=\alpha +\beta u\)的斜率和截距的最小二乘估计分别为\(\hat{\beta }=\dfrac{\sum\limits_{i=i}^{n}{\left( {{u}_{i}}-\overline{u} \right)\left( {{v}_{i}}-\overline{v} \right)}}{\sum\limits_{i=i}^{n}{{{\left( {{u}_{i}}-\overline{u} \right)}^{2}}}},\hat{\alpha }=\overline{v}-\hat{\beta }\overline{u}\) .