MHT CET · Maths · Vector Algebra
If \(\bar{a}=\hat{i}+2 \hat{j}-3 \hat{k}, \bar{b}=3 \hat{i}+\hat{j}+2 \hat{k}, \bar{c}=\hat{i}+3 \hat{j}+\hat{k}\) and \(\bar{a}+\lambda \bar{b}\) is perpendicular to \(\overline{\mathrm{c}}\), then \(\lambda=\)
- A -2
- B 4
- C -4
- D 2
Answer & Solution
Correct Answer
(A) -2
Step-by-step Solution
Detailed explanation
\(
\begin{aligned}
& \bar{a}+\lambda \bar{b}=(\hat{i}+2 \hat{j}-3 \hat{k})+\lambda(3 \hat{i}-\hat{j}+2 \hat{k}) \\
& =(1+3 \lambda) \hat{i}+(2-\lambda) \hat{j}+(-3+2 \lambda) \hat{k}
\end{aligned}
\)
Since \(\overline{\mathrm{a}}+\lambda \overline{\mathrm{b}}\) is \(\perp\) er to \(\overline{\mathrm{c}}\), we write
\(
\begin{aligned}
& (1)(1+3 \lambda)+(3)(2-\lambda)+(1)(-3+2 \lambda) \\
& \therefore 1+3 \lambda+6-3 \lambda-3+2 \lambda=0 \Rightarrow \lambda=-2
\end{aligned}
\)
\begin{aligned}
& \bar{a}+\lambda \bar{b}=(\hat{i}+2 \hat{j}-3 \hat{k})+\lambda(3 \hat{i}-\hat{j}+2 \hat{k}) \\
& =(1+3 \lambda) \hat{i}+(2-\lambda) \hat{j}+(-3+2 \lambda) \hat{k}
\end{aligned}
\)
Since \(\overline{\mathrm{a}}+\lambda \overline{\mathrm{b}}\) is \(\perp\) er to \(\overline{\mathrm{c}}\), we write
\(
\begin{aligned}
& (1)(1+3 \lambda)+(3)(2-\lambda)+(1)(-3+2 \lambda) \\
& \therefore 1+3 \lambda+6-3 \lambda-3+2 \lambda=0 \Rightarrow \lambda=-2
\end{aligned}
\)
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