# trig

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Suppose sin theda= – 3/5 and theda is a Quadrant III angle.

Find the exact value of sin 2 theda and cos 2 theda.

• trig -

It is theta not theda. Quadrant III= a reflex angle greater than 180 degrees and yet less than or = to 270 degrees.

• trig -

as measured counterclockwise from the origin (0,0).

• trig -

since sinØ = -3/5, in the third quad cosØ = -4/5

sin 2Ø = 2sinØcosØ = 2(-3/5)(-4/5) = 24/25
cos 2Ø = cos^2 Ø - sin^2 Ø = 16/25 - 9/25 = 7/25

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