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!