What is the measure of angle #x# in the interval #180° <= x <=270°# that satisfies the equation #2cos(x) + 1 =0#?

1 Answer
Nghi N.
Apr 9, 2016

#(4pi)/3 or 240^@#

Explanation:

Solve trig equation:
2cos x + 1 = 0
#cos x = - 1/2#
Trig table , trig unit circle give -->
#cos x = - 1/2# --> #x = +- (2pi)/3#
The co-terminal arc of #(-2pi)/3# --> #(2pi - (2pi)/3 = (4pi)/3)#
Answer in the interval (180, 270):
#(4pi)/3, or 240^@#

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