`cos(theta) = -sqrt(2)/2` Find two solutions of each equation. Give your answers in degrees (0 <= theta <= 360) and radians (0 <= theta <= 2pi)

Textbook Question

Chapter 4, 4.4 - Problem 92b - Precalculus (3rd Edition, Ron Larson).
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nisarg's profile pic

nisarg | Student, Grade 11 | (Level 1) Valedictorian

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Sine and cosine at max are 1.  Cosine is X and Sine is Y. The values of them repeat as their graphs are waves. As you can see here 

 So here `3pi/4`   and `5pi/4`   can both equal theta

theta can be 135 degrees or it can be 225 degrees

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kspcr111's profile picture

kspcr111 | In Training Educator

Posted on

The above solution is right 

this is the continuation


radians the 

value of `theta = (3pi)/4 and (5pi)/4`

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Wiggin42 | Student, Undergraduate | (Level 2) Valedictorian

Posted on

`cos(theta)` is negative in the 2nd and 3rd quadrants. Looking at a unit circle, the values of theta that satisfy this are 135 and 225 degrees. 


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