本帖最后由 isee 于 2021-6-15 22:58 编辑
算是传统了
17. 已知平面向量`\vv{a},\vv{b},\vv{c},(\vv{c}\ne 0)`满足`\left| \vv{a} \right|=1,\left| \vv{b} \right|=2,\vv{a}\cdot \vv{b}=0,\left( \vv{a}-\vv{b} \right)\cdot \vv{c}=0`. 记向量$\vv{d}$在$\vv{a},\vv{b}$方向上投影分别为`x`,`y`,`\vv{d}-\vv{a}`在$\vv{c}$方向上的投影为`z`,则$x^2+y^2+z^2$的最小值为___________. |