Algebra II

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Find all values of theta given that theta is between 0 degrees and 360 degrees. It is known that cos theta = -√3
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2

• Algebra II -

Timmy, Ryland, Cobra, Timmy -- you must be having an identity crisis tonight.

• Algebra II -

cosØ = -√3/2

1. find the reference angle
(using the positive result √3/2 , use inverse cos to get and angle of 30°
( Make yourself familiar with the ratio of sides of the 30-60-90 triangle)
2. Where is the angle Ø ?
Since the cosine is negative in II and III
in II : Ø = 180-30 or 150°
or
in III : Ø = 180+30 = 210°

• Algebra II -

oh so we only want reference angle. i thought values meant sin,cos,and tan. how do you know it only wanted reference angle?

• Algebra II -

didn't it say,
"Find the values of Ø" , not find the values of sinØ etc ?

Finding the reference angle is only the first step, from there you have to decide what to do with that reference angle depending on the position of Ø and the values of cosØ

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