Câu hỏi
\(\left( d \right):\,\,x + y + 1 = 0.\,\,A\left( {3;1} \right).\) Tìm \(M \in \left( d \right)\) để \(AM = \sqrt {13} \).
- A \(\left[ \begin{array}{l}M\left( {0; - 1} \right)\\M\left( {1; - 2} \right)\end{array} \right.\)
- B \(\left[ \begin{array}{l}M\left( {0;1} \right)\\M\left( {1;2} \right)\end{array} \right.\)
- C \(\left[ \begin{array}{l}M\left( {0;1} \right)\\M\left( {2;1} \right)\end{array} \right.\)
- D \(\left[ \begin{array}{l}M\left( {1;0} \right)\\M\left( {2;1} \right)\end{array} \right.\)
Lời giải chi tiết:
Giả sử \(M\left( {a;b} \right).\,\,M \in \left( d \right) \Rightarrow a + b + 1 = 0 \Rightarrow b = - 1 - a\,\,\,\left( 1 \right)\)
\(AM = \sqrt {13} \Leftrightarrow {\left( {a - 3} \right)^2} + {\left( {b - 1} \right)^2} = 13\,\,\,\left( 2 \right)\)
Thay (2) vào (1) \( \Rightarrow {\left( {a - 3} \right)^2} + {\left( {a + 2} \right)^2} = 13 \Rightarrow {a^2} - a = 0 \Leftrightarrow \left[ \begin{array}{l}a = 0\\a = 1\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}M\left( {0; - 1} \right)\\M\left( {1; - 2} \right)\end{array} \right.\).
Chọn A.