Question

 Cho đường thẳng d \(\left\{{}\begin{matrix}x=-2+t\\y=-1+3t\end{matrix}\right.\) Tìm điểm \(A\in d\) ,\(AB=\sqrt{10}\) với B (2;1)

Answer 1

\(A\in d\Rightarrow A\left(-2+t;-1+3t\right)\)

\(AB=\sqrt{10}\Leftrightarrow\sqrt{\left(-2+t-2\right)^2+\left(-1+3t-1\right)^2}=\sqrt{10}\)

\(\Leftrightarrow\left(t-4\right)^2+\left(3t-2\right)^2=10\\ \Leftrightarrow t^2-8t+16+9t^2-12t+4=10\\ \Leftrightarrow10t^2-20t+20=10\\ \Leftrightarrow t^2-2t+1=0\Leftrightarrow\left(t-1\right)^2=0\Leftrightarrow t=1\)

\(\Rightarrow A\left(-1;2\right)\).