Question

If vectors P. Q and R have magnitude 5, 12 and 13 units $\overrightarrow{P}+\overrightarrow{Q}=\overrightarrow{R}$, the angle between Q and R is

• A. $co{s}^{-1}\frac{5}{12}$
• B. $co{s}^{-1}\frac{5}{13}$
• C. $co{s}^{-1}\frac{12}{13}$
• D. $co{s}^{-1}\frac{7}{13}$

Answer 1

The correct option is C $co{s}^{-1}\frac{12}{13}$

$|\overrightarrow{P}|=5,|\overrightarrow{Q}|=12$ and $|\overrightarrow{R}|=13$
$\cos \theta =\frac{Q}{R}=\frac{12}{13}$
$\therefore \theta ={\cos }^{-1}\left(\frac{12}{13}\right)$