The angle between vectors a and b is 45. If |a| =5 units and |b| =4 units, find the value of |a-b| and of |a+b|
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Originally Posted by Trefoil2727 The angle between vectors a and b is 45. If |a| =5 units and |b| =4 units, find the value of |a-b| and of |a+b| Think of as adjacent sides of a parallelogram.
Then is the diagonal opposite the angle between them. is the diagonal opposite the angle adjacent to the angle between them.
Now use the law of cosines.
I hope that you know that and .
And you should know that where is the angle between a and b.
I see Plato got in just ahead of me. Different points of view about the same thing.
but why a.b=|a||b|cos θ?
Originally Posted by Trefoil2727 but why a.b=|a||b|cos θ? If you have to ask, then you are in no way ready to do this question.
Why then were you asked to work this question?
still can't find a+b..
I don't know, maybe my teacher likes to make his students suffer
hah, got it! thanks!
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