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Find the projection of vector \(\vec{b}=2\hat{i}+2\sqrt{2} \,\hat{j}-2\hat{k}\) on the vector \(\vec{a}=\hat{i}-\hat{j}-\sqrt{2} \,\hat{k}\).(a) 2(b) \(\sqrt{2}\)(c) 1(d) \(2\sqrt{2}\)I had been asked this question in an interview.The doubt is from Product of Two Vectors-1 topic in division Vector Algebra of Mathematics – Class 12

Answer» RIGHT answer is (B) \(\sqrt{2}\)

For explanation: The projection of VECTOR \(\vec{b}\) on the vector \(\vec{b}\) is GIVEN by \(\frac{1}{|\vec{a}|} (\vec{a}.\vec{b})\)

\(|\vec{a}|=\sqrt{(1)^2+(-1)^2+(-\sqrt{2})^2}=\sqrt{1+1+2}=\sqrt{4}\)=2

Also, \(\vec{a}.\vec{b}=2(1)+2\sqrt{2} \,(-1)-2(-\sqrt{2})=2-2\sqrt{2}+2\sqrt{2}\)=2

Therefore, the projection of vector \(\hat{i}-\hat{j}-\sqrt{2} \,\hat{k}\) on the vector \(\vec{b}=2\hat{i}+2\sqrt{2}\hat{j}-2\hat{k}\)is

\(\frac{1}{|\vec{a}|} (\vec{a}.\vec{b})=\frac{1}{2}\) (2)=1.


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