Find the exact soultions on the interval from (-90degrees, 720degrees) cos3x=-sqrt3/2?

1 Answer
Kalyanam S.
Jul 8, 2018

#color(indigo)(x = 50^@, 70^@, 170^@, 190^@#, #color(crimson)(-90^@ < x < 720^@#

Explanation:

#cos 3x = - sqrt3 / 2#

Cosine is negative in II & III Quadrants only.

#3x = cos ^1 (-sqrt3/2) = 150^@, 210^@, 510^@, 570^@#

#color(indigo)(x = 50^@, 70^@, 170^@, 190^@#, #color(crimson)(-90^@ < x < 720^@#

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