Question

If $0.4\hat{i}+0.8\hat{j}+c\hat{k}$ represents a unit vector then $c$ is

• A. $\pm \sqrt{0.2}$
• B. $\sqrt{0.2}$
• C. $\sqrt{0.8}$
• D. $0$

Answer 1

The correct option is A $\pm \sqrt{0.2}$

Given vector is unit vector so its magnitude should be $1$

S0 $1=\sqrt[2]{2{0.4}^2+{0.8}^2+c^2}$ or $c^2=0.2$ or $c=\pm \sqrt[2]{20.2}$