9. II: Note that .
Section B
Number 9) II
How do go about answering this?
Please see attached pdf
What i did
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cos2x=1-2sin^{2}75
cos 2x = cos (x+x)
cos (x+x) = cosA*CosB-SinA*SinB
cos( 60 + 90)= cos60*cos90 - sin60*cos90
answer i got was wrong
section B part III number 9
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cos 2x = cos^{2}x - sin^{2}x
cos( x + x) = cosA*CosB-SinA*SinB
cos(90 + 45)= cos90*cos45-sin90*sin45
I attempted this one similarly.. wrong answer... help!
Oh okay, I was a little confused with the 45/60 thing.
Also, , not . The sine/cosine of an angle can only be from -1 to 1 inclusive. Since is outside the set [-1,1], this answer cannot be correct.