本帖最后由 realnumber 于 2017-12-30 17:50 编辑
继续1楼的解答,
$\abs{(\vv{a}+\vv{b})·\vv{n}}=\abs{16x+32y}---(1)$
又$\abs{\vv{n}}=1$,得到$16x^2+32y^2+z^2=1----(2)$,
又夹角30度得到$\cos{30\du}=\frac{16x}{4},x=\frac{\sqrt{3}}{8}$
(1)简化为$\abs{(\vv{a}+\vv{b})·\vv{n}}=\abs{16x+32y}=\abs{2\sqrt{3}+32y}---(1')$
(2)简化为$32y^2+z^2=0.25$----(2')这样令z=0,$y=\frac{\sqrt{2}}{16}$,(1')取最大. |