搜尋結果
5 天前 · 解答: \cases {L_1:x+my=0\\ L_2:m (x-1)+3=y} \Rightarrow \cases {A (0,0)\\ B (1,3)\\ L_1\bot L_2 } \Rightarrow \overline {PA}\cdot \overline {PB}最大值出現在\overline {PA}= \overline {PB} \\ 假設\overline {PA}= a \Rightarrow 2a^2=\overline {AB}^2=10 \Rightarrow \overline {PA}\cdot \overline {PB}=a^2= \bbox [red, 2pt]5.
