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Need Solution for R.D.Sharma Maths Class 12 Chapter 23 Scalar or Dot  Products  Exercise 23.1 Question 27 Maths Textbook Solution.

Answers (1)

Answer:  Proved

Hint:  You must know the rules of solving vectors.

Given:  If \vec{a}=5\hat{i}-\hat{j}-3\hat{k} and \vec{b}=\hat{i}+3\hat{j}-5\hat{k} then show that the vectors \vec{a}+\vec{b} and \vec{a}-\vec{b} are orthogonal.

Solution: \vec{a}=5\hat{i}-\hat{j}-3\hat{k} and \vec{b}=\hat{i}+3\hat{j}-5\hat{k}

\begin{aligned} \therefore \vec{a}+\vec{b}=5 \hat{\imath}-\hat{\jmath}-3 \hat{k}+\hat{\imath}+3 \hat{\jmath}-5 \hat{k} \\ \end{aligned}

                                                                                \begin{aligned} \vec{a}+\vec{b}=6 \hat{i}+2 \hat{\jmath}-8 \hat{k} \end{aligned}

And

\begin{aligned} &\vec{a}-\vec{b}=5 \hat{\imath}-\hat{\jmath}-3 \hat{k}-\hat{\imath}+3 \hat{j}-5 \hat{k} \\\\ &\vec{a}-\vec{b}=4 \hat{\imath}-4 \hat{\jmath}+2 \hat{k} \\ \end{aligned}

Now,

\begin{aligned} &(\vec{a}+\vec{b}) \cdot(\vec{a}-\vec{b})=(6 \hat{\imath}+2 \hat{\jmath}-8 \hat{k}) \cdot(4 \hat{\imath}-4 \hat{\jmath}+2 \hat{k}) \\\\ &(\vec{a}+\vec{b}) \cdot(\vec{a}-\vec{b})=24-8-16 \end{aligned}

\left ( \vec{a}.\vec{b} \right ) . \left ( \vec{a}-\vec{b} \right )=0

So,\vec{a}+\vec{b}is orthogonal of \vec{a}-\vec{b}

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