Question

The direction cosines of vector $\mathbf{a} = 3\mathbf{i} + 4\mathbf{j} + 5\mathbf{k}$ in the direction of positive axis of x, is

• A. $\pm \frac{3}{\sqrt{50}}$
• B. $\frac{4}{\sqrt{50}}$
• C. $\frac{3}{\sqrt{50}}$
• D. $- \frac{4}{\sqrt{50}}$

Answer 1

Answer: (C)

$\frac{3}{\sqrt{50}}$

Answer 2

$\frac{3}{\sqrt{3^{2} + 4^{2} + 5^{2}}} = \frac{3}{\sqrt{50}}.$