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

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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

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Answers (2)

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

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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

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Comments (3)

Dileep kumar

12th Apr, 2019

Thanks

Reply

Dileep kumar

12th Apr, 2019

But the answer given is 120

Reply

Akash Pal

12th Apr, 2019

The second one is the correct answer

Reply

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