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If three unit vectors a, b, c satisfy a+b+c=0 then the angle between a and b


Dileep kumar 12th Apr, 2019
Answers (2)
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Akash Pal 12th Apr, 2019

a+b+c=0

a+b=-c

|a+b|=|c|

a²+b²+2abcos∆=|c|²

1+1+2cos∆=1

cos∆= -1

∆=π

user-img
Akash Pal 12th Apr, 2019

Hello Dileep, I am glad to help you.

a+b+c=0

a+b=-c

|a+b|=|c|

a²+b²+2abcos∆=|c|²

9+25+30cos∆=49

cos∆=1/2

∆=π/3 = 60°


I think your doubt is clear now.

All the best.

3 Comments
Comments (3)
12th Apr, 2019
Thanks
Reply
12th Apr, 2019
But the answer given is 120
Reply
12th Apr, 2019
The second one is the correct answer
Reply

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