1.

Find the projection of vector (8i + j) in the direction of vector (i + 2j - 2k).

Answer»

Let,

 \(\vec{a} =( \vec{8i} + \vec{j})\)

\(\vec{b} = (\vec{i} + \vec{2j} - \vec{2k})\)

\(\vec{b}\) = \(\sqrt{1^2 + 2^2+ 2^2}\) = \(\sqrt{1+ 4+ 4}\) = \(\sqrt {9}\) = 3

 \(\vec{b}\) = \(\frac{\vec{b}}{\vec{|b|}}\) = \(\frac{\vec{i}+\vec{2j}-\vec{2k}}{3}\) 

∴ The projection of \((\vec{8i}+\vec{j})\) on \((\vec{i}+{2j}-\vec{2k})\) is   \((\vec{8i}+\vec{j})\)   \(\frac{\vec{i}+\vec{2j}-\vec{2k}}{3}\) 

\(\frac{8+2+0}{3}\) = \(\frac{10}{3}\)



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