Find the exact value for cos 105 degrees (No credit for a decimal answer from a calculator!)
thank you very much!:)
Find the exact value for cos 105 degrees (No credit for a decimal answer from a calculator!)
thank you very much!:)
You know the basic identities?
Well, you'll use them here.
What is 105?
It is 45 + 60.
So,
but cos(A+B) = cos A cosB - sin A sin B[/math]
So, cos (105) = cos (45+60) = cos 45 cos 60 - sin 45 sin 60
Can you do it now? :)
Yes thank you very much!
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