Jawabanmu

2013-12-14T09:58:58+07:00
A =   \left[\begin{array}{ccc}3\\-2\\1\end{array}\right]
b =  \left[\begin{array}{ccc}2\\y\\2\end{array}\right] 

 \frac{a.b}{|b|} =  \frac{1}{2} |b|
3.2 + (-2).y + 1.2 = \frac{1}{2} \sqrt{2^{2} + y^{2} + 2^{2}} \sqrt{2^{2} + y^{2} + 2^{2}}
6 -2y + 2 = \frac{1}{2} (2^{2} + y^{2} + 2^{2})
-2y + 8 = \frac{1}{2} (y^{2} + 8)
-2y + 8 = \frac{y^{2}}{2} + 4
\frac{y^{2}}{2} + 2y - 4 = 0
y^{2} + 4y - 8 = 0