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Explain solution RD Sharma class 12 chapter Vector or Cross Product exercise 24.1 question 4 maths

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Answer         :  \sqrt{74}
Hint              : To solve this equation we suppose both terms in x and y then we use magnitude formula            

Given           :\vec{a}=(3 \hat{k}+4 \hat{\jmath}) \times(\hat{\imath}+\hat{\jmath}-\hat{k})

Solution       :

\begin{aligned} &\vec{x}=3 \hat{k}+4 \hat{j} \\\\ &\vec{y}=\hat{\imath}+\hat{\jmath}-\hat{k} \end{aligned}

\begin{aligned} &|\vec{x} \times \vec{y}| \\ &\vec{x} \times \vec{y}=\left|\begin{array}{ccc} \hat{\imath} & \hat{\jmath} & \hat{k} \\ 0 & 4 & 3 \\ 1 & 1 & -1 \end{array}\right| \end{aligned}

\begin{aligned} &=\hat{\imath}(4 \times-1-3 \times 1)-\hat{\jmath}(0 \times 1-3 \times 1)+\hat{k}(0 \times 1-41) \\ &=-7 \hat{\imath}+3 \hat{\jmath}-4 \hat{k} \\\\ &|\vec{x} \times \vec{y}|=\sqrt{(-7)^{2}+3^{2}+(-4)^{2}} \\\\ &=\sqrt{49+9+16} \\\\ &\vec{a}=\sqrt{74} \end{aligned}

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