Solve the Following equation on the interval [0,2pi].

Question

Cos x + 0.75=0

Provide an approximate answer to two decimal places.

Answer 1

Cosx + .75 = 0

Cosx = -.75

x = Cos^-1(.75)

use a calculator with an inverse cosine function

x = about 180-41.41 = 138.59 degrees

or 180+41.41 = 221.41 degrees

41.41 is the reference angle

x is in quadrant II and III where cosines are negative