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If \(\vec{a}=2\hat{i}+3\hat{j}+4\hat{k}\) and \(\vec{b}=4\hat{i}-2\hat{j}+3\hat{k}\). Find \(|\vec{a}×\vec{b}|\).(a) \(\sqrt{685}\)(b) \(\sqrt{645}\)(c) \(\sqrt{679}\)(d) \(\sqrt{689}\)The question was posed to me in an online quiz.I want to ask this question from Product of Two Vectors-2 topic in division Vector Algebra of Mathematics – Class 12

Answer»

Correct CHOICE is (b) \(\sqrt{645}\)

To explain: GIVEN that, \(\vec{a}=2\hat{i}+3\hat{J}+4\hat{k}\) and \(\vec{b}=4\hat{i}-2\hat{j}+3\hat{k}\)

∴ \(\vec{a}×\vec{b}=\begin{vmatrix}\hat{i}&\hat{j}&\hat{k}\\2&3&4\\4&-2&3\end{vmatrix}\)

=\(\hat{i}(9—8)-\hat{j}(6-16)+\hat{k}(-4-12)\)

=\(17\hat{i}+10\hat{j}-16\hat{k}\)

∴\(|\vec{a}×\vec{b}|=\sqrt{17^2+10^2+(-16)^2}\)

=\(\sqrt{289+100+256}\)

=\(\sqrt{645}\)



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