SOLUTION: Find the exact value of cosine 2 theta given sine of theta = negative 3 over 8 and theta is between 270 degrees and 360 degrees.

Question 945484: Find the exact value of cosine 2 theta given sine of theta = negative 3 over 8 and theta is between 270 degrees and 360 degrees.
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
Find the exact value of cosine 2 theta given sine of theta = negative 3 over 8 and theta is between 270 degrees and 360 degrees.
***
Identity: cos(2x)=1-2sin^2(x)
sinx=(-3/8)
sin^2(x)=9/64
cos(2x)=1-2(9/64)=1-18/64=46/64
..
Check:
sinx=-3/8 (Q4)
x≈337.97
2x≈675.95˚
cos(2x)=cos(675.95˚)≈0.7187..
exact value as computed=46/64≈0.7187..
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