Question 877877
Question 1. 2cosx^4 -3cosx^2 +1=0
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(2cos^2 - 1)*(cos^2 - 1) = 0
cos^2 = 1/2, etc
cos^2 = 1, etc
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#2 is similar
#3 is easy
#4 is similar
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Question 5. 2sinxcosx=1
sin(2x) = 1
2x = 90 degs