knowing the length of 2 sides and angle between 2 sides, how to get the length of third side?
- Thread starter motorhero
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Use law of cosines to calculate the required length.
Try not to use calculator and you should get an answer involving \(\displaystyle \sqrt{}\)
forgive my silly question, I do not know how Cos (120) can be used with the other 2 lengths and come out as an integer. I think that is what you mean law of cosines, but I have no clue. Can you please give more details? thank you.
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What is the value of cos(120)?
COS 120. I think that is the proper way to write it.
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What is the value of COS 120?
0.81418097052
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AvgStudent
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That is correct.
AvgStudent
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Shouldn't it be [imath]\sqrt{7}?[/imath]
[math]c=\sqrt{a^2+b^2-2ab\cos(\theta)}=\sqrt{2^2+1^2-2(2)(1)(-.5)}=\sqrt{4+1+2}=\sqrt{7}[/math]
[math]c=\sqrt{a^2+b^2-2ab\cos(\theta)}=\sqrt{2^2+1^2-2(2)(1)(-.5)}=\sqrt{4+1+2}=\sqrt{7}[/math]
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motorhero said:
COS 120=-0.5, then c is square root of 9.
thank you.
so I know COS120 I will know the right answer. thank you.
Somehow the response kept getting "changed" and I may have misread it with my sleepy eyes.
Yes the answer should be \(\displaystyle \sqrt{7}\)