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Explain Solution R.D.Sharma Class 12 Chapter 25 Scalar Triple Product Exercise 25.1 Question 15 Maths Textbook Solution.

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Answer :-   24 cubic units

Hint :- Use formula of volume of parallelopiped =\left [ \vec{a}\: \: \vec{b}\: \: \vec{c} \right ] where, \vec{a}\: \: \vec{b}  &  \: \: \vec{c} be the adjacent edges.

Given:\begin{aligned} &2 \vec{a}=2(\hat{\imath}-\hat{\jmath}+2 \hat{k})=2 \hat{\imath}-2 \hat{\jmath}+4 \hat{k} \\ \end{aligned}

\begin{aligned} &-\vec{b}=-(3 \hat{\imath}+4 \hat{\jmath}-5 \hat{k})=-3 \hat{\imath}-4 \hat{\jmath}+5 \hat{k} \\ &3 \vec{c}=3(2 \hat{\imath}-\hat{\jmath}+3 \hat{k})=6 \hat{\imath}-3 \hat{\jmath}+9 \hat{k} \end{aligned}

∴ Volume of parallelopiped  =\mid \left [ 2\vec{a}\left ( -\vec{b} \right ) \left ( 3\vec{c} \right )\right ]\mid

=\left|\begin{array}{ccc} 2 & -2 & 4 \\ -3 & -4 & 5 \\ 6 & -3 & 9 \end{array}\right|

\begin{aligned} &=2(-36+15)+2(-27-30)+4(9+24) \\\\ &=2(-21)+2(-57)+4(33) \\\\ &=-42-114+132 \\\\ &=-24 \end{aligned}

∴ Volume of parallelopiped =\mid -24\mid =24 cubic units .

 

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