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Need Solution for R.D.Sharma Maths Class 12 Chapter 23 Scalar or Dot  Products  Exercise 23.1 Question 34 Maths Textbook Solution.

Answers (1)

Answer6\hat{i}+2\hat{k},-\hat{i}-2\hat{j}+3\hat{k}

Hint: You must know the rules of solving vectors.

Given:   Express the vector \vec{a}=5\hat{i}-2\hat{j}+5\hat{k}  as the sum of the two vectors such that one is parallel to vector \vec{b}=3\hat{i}+\hat{k} and other is perpendicular to \vec{b}.

Solution: Given that,

\vec{a}=5\hat{i}-2\hat{j}+5\hat{k} and \vec{b}=3\hat{i}+\hat{k}

Let \vec{x}. and \vec{y}. be such that

\begin{aligned} &\vec{a}=\vec{x}+\vec{y} \\\\ &\vec{y}=\vec{a}-\vec{x} \rightarrow(1) \\ \end{aligned}

Since, \vec{x}.is parallel to \vec{b}.

\begin{aligned} &\vec{x}=t(3 \hat{\imath}+\hat{k}) \\\\ &\vec{x}=3 t \hat{\imath}+t \hat{k} \\ \end{aligned}

Substituting the values, \vec{x}. and \vec{a}.

\begin{aligned} &\vec{y}=5 \hat{\imath}-2 \hat{\jmath}+5 \hat{k}-3 t \hat{\imath}+t \hat{k} \\\\ &\vec{y}=(5-3 t) \hat{\imath}-2 \hat{\jmath}+(5-t) \hat{k} \\ \end{aligned}

Since \vec{y}. is perpendicular to  \vec{b}.

\begin{aligned} &\vec{y} \cdot \vec{b}=0 \\ &{[(5-3 t) \hat{\imath}-2 \hat{\jmath}+(5-t) \hat{k}] \cdot 3 \hat{\imath}+\hat{k}=0} \\ &3(5-3 t)+0+(5-t)=0 \\ &15-9 t+5 t=0 \\ &20-10 t=0 \\ &t=2 \end{aligned}

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