Question #83317

1 Answer
Nghi N
Jan 22, 2018

#x = +- pi/8 + kpi#
#x = +- (3pi)/8 + kpi#

Explanation:

#2cos^2 2x = 1#
#cos^2 2x = 1/2#
#cos 2x = +- sqrt2/2#
Solve the above basic trig equations using trig table and unit circle:
a. #cos 2x = sqrt2/2#
Unit circle give 2 solutions -->
#2x = +- pi/4 + 2kpi#
#x = +- pi/8 + kpi#
b. #cos 2x = - sqrt2/2#
#2x = +- (3pi)/4 + 2kpi#
#x = +- (3pi)/8 + kpi#

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