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Provide solution for RD Sharma Maths Class 12 Chapter 25 Scale Triple Product Exercise Very Short Answer Question, question 2.

Answers (1)

Answer:

2

Hint:

Use scalar triple product formula.

Given:

\left[\begin{array}{lll} \hat{i}+\hat{j} & \hat{j}+\hat{k} & \hat{k}+\hat{i} \end{array}\right]

Solution:

\begin{aligned} &{[\hat{i}+\hat{j} \hat{j}+\hat{k} \hat{k}+\hat{i}]} \\ &=(\hat{i}+\hat{j}) \cdot\{(\hat{j}+\hat{k}) \times(\hat{k}+\hat{i})\} \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \quad[\because[\overrightarrow{\boldsymbol{a}} \overrightarrow{\mathbf{b}} \overrightarrow{\boldsymbol{c}}]=\overrightarrow{\boldsymbol{a}} \cdot(\overrightarrow{\boldsymbol{b}} \times \overrightarrow{\boldsymbol{c}})] \\ &=(\hat{\boldsymbol{\imath}}+\hat{\boldsymbol{j}}) \cdot\{(\hat{\boldsymbol{j}} \times \hat{\boldsymbol{k}})+(\hat{\boldsymbol{j}} \times \hat{\boldsymbol{\imath}})+(\widehat{\boldsymbol{k}} \times \widehat{\boldsymbol{k}})+(\widehat{\boldsymbol{k}} \times \hat{\boldsymbol{\imath}})\} \end{aligned}

\begin{aligned} &=(\hat{i}+\hat{j}) \cdot(\hat{i}+(-\hat{k})+0+\hat{j}) \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \quad\left[\begin{array}{l} \because \hat{\boldsymbol{j}} \times \widehat{\boldsymbol{k}}=\hat{\boldsymbol{\imath}}, \hat{\boldsymbol{j}} \times \hat{\boldsymbol{\imath}}=-\widehat{\boldsymbol{k}} \\ \hat{\boldsymbol{k}} \times \widehat{\boldsymbol{k}}=\mathbf{0}, \widehat{\boldsymbol{k}} \times \hat{\boldsymbol{\imath}}=\hat{\boldsymbol{j}} \end{array}\right] \\ &=(\hat{i}+\hat{j}) \cdot(\hat{i}-\hat{k}+\hat{j}) \\ &=(\hat{i} \hat{i})-(\hat{i} \hat{k})+(\hat{i} \cdot \hat{j})+(\hat{j} \hat{i})-(\hat{j} \hat{k})+(\hat{j} \cdot \hat{j}) \end{aligned}

\begin{aligned} &=1-0+0+0-0+1 \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \quad[\because \hat{\imath} . \hat{\boldsymbol{\imath}}=\hat{\boldsymbol{\jmath}} \cdot \hat{\boldsymbol{j}}=\mathbf{1}, \hat{\boldsymbol{\imath}} . \widehat{\boldsymbol{k}}=\hat{\boldsymbol{\imath}} . \hat{\boldsymbol{\jmath}}=\hat{\boldsymbol{\jmath}} \cdot \hat{\boldsymbol{\imath}}=\hat{\boldsymbol{\jmath}} \cdot \widehat{\boldsymbol{k}}=\mathbf{0}] \\ &=2 \end{aligned}

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