Question

Trig///HELPP PLEASE!! i’ve been stuck on this for 30 minutes!!

Answer 1

Answer: There are two solutions and they are

theta = 135

theta = 225

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Explanation:

Recall that x = cos(theta). Since the given cosine value is negative, this indicates x < 0. Theta is somewhere to the left of the y axis, placing it in quadrant 2 or quadrant 3.

It turns out there are two solutions, with one solution per quadrant mentioned above. Use the unit circle to find that the two solutions are:

theta = 135

theta = 225

You're looking for points on the unit circle that have x coordinate equal to x = -sqrt(2)/2. Those two points correspond to the angles of 135 and 225, which are in quadrants 2 and 3 respectively.

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I recommend using your calculator to note that

-sqrt(2)/2 = -0.70710678

cos(135) = -0.70710678

cos(225) = -0.70710678

The decimal values are approximate. Make sure your calculator is in degree mode. Because those three results are the same decimal approximation, this indicates that cos(135) = cos(225) = -sqrt(2)/2.