A) \[\frac{\pi }{3}\]
B) \[\frac{\pi }{4}\]
C) \[\frac{\pi }{6}\]
D) \[\frac{\pi }{2}\]
Correct Answer: A
Solution :
Let\[a+b+c=0\Rightarrow (a+b)=-c\] \[\Rightarrow \]\[{{(a+b)}^{2}}={{c}^{2}}\] \[\Rightarrow \]\[{{a}^{2}}+{{b}^{2}}+2a.b={{c}^{2}}\] \[\Rightarrow \]\[9+25+2.3.5\cos \theta =49\] \[\left( \because \left| \overset{\to }{\mathop{a}}\, \right|=3,\left| \overset{\to }{\mathop{b}}\, \right|=5\,\text{and}\left| \overset{\to }{\mathop{c}}\, \right|=7 \right)\] \[\therefore \]\[\cos \theta =\frac{1}{2}\Rightarrow \theta =\frac{\pi }{3}\]You need to login to perform this action.
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