Question #ca68e

1 Answer
bp
Aug 13, 2017

#Cos 120= -1/2#

Explanation:

First of all make out the Quarter in which the angle lies. Now 120 degree angle falls in IInd Quarter in which the sign of cosine function is negative.

Next make out the acute angle which the direction of the given angle makes with x-axis. In the present case of angle of 120 degree, the acute angle will be 60 degrees. The cosine of 60 degree is #1/2#.

Combining both the conclusions above, cos 120 degrees would be #-1/2#

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