cos^2theta(1-cos^2)=cos^2
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2cos2x−1) -->
2cos2x−1=cos2x−12
cos2x=1−12=12
cosx=±1√2=±√22
Trig table and unit circle give -->
a. cosx=√22 --> x=±π4
b. cosx=−√22 --> x=±3π4
Answers for (0,2π) -->
π4,3π4,5π4,7π4
Note. Arc −π4 is co-terminal to arc 7π4
Arc −3π4 is co-terminal to arc 5π4
2cos2x−1=cos2x−12
cos2x=1−12=12
cosx=±1√2=±√22
Trig table and unit circle give -->
a. cosx=√22 --> x=±π4
b. cosx=−√22 --> x=±3π4
Answers for (0,2π) -->
π4,3π4,5π4,7π4
Note. Arc −π4 is co-terminal to arc 7π4
Arc −3π4 is co-terminal to arc 5π4
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