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Vectors> If a+b+c=0 and |a|=3,|b|=5,|c|=7, then an...

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If a+b+c=0 and |a|=3,|b|=5,|c|=7, then angle between vectors a and b is??

Mani kandan , 7 Years ago

Grade 12th pass

1 Answers

Ashik Raveendran

$a + b +c =0$

then, $a + b =-c$

taking modulus on both sides , $\left |a+b \left | = \left | -c \right |$

$\Rightarrow \left | a+b \right |^{2}=\left | -c^{} \right |^{2}$

$a^{2}+2\vec{a}\vec{b}+b^{2}=c^{2}$

$abcos\theta =c^{2}-a^{2}-b^{2}$

$\Rightarrow cos\theta =c^{2}-a^{2}-b^{2}/2ab$

substituting the values we get , $cos\theta =1/2$

$\Rightarrow \theta =60^{o}$

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Last Activity: 7 Years ago

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