Vector Algebra Question 328
Question: If $ |\mathbf{a}|,=3,|\mathbf{b}|,=4,|\mathbf{c}|,=5 $ and $ \mathbf{a}+\mathbf{b}+\mathbf{c}=0, $ then the angle between a and b is
[MP PET 1989; Bihar CEE 1994]
Options:
A) 0
B) $ \frac{\pi }{6} $
C) $ \frac{\pi }{3} $
D) $ \frac{\pi }{2} $
Show Answer
Answer:
Correct Answer: D
Solution:
- $ \mathbf{a}+\mathbf{b}=-,\mathbf{c} $
$ \Rightarrow |\mathbf{a}{{|}^{2}}+|\mathbf{b}{{|}^{2}}+2|\mathbf{a}||\mathbf{b}|\cos \theta =|\mathbf{c}{{|}^{2}} $
$ \Rightarrow \cos \theta =0\Rightarrow \theta =\frac{\pi }{2}. $
BETA
