Trig exact values

Find the exact value of sin 195° given sin 195°=sin (225°-30°)

Basically what I need to know is how sin 225° = -sin 45°....how do I know that sin 225° is equal to -sin 45°?

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Originally Posted by Ericonda

Find the exact value of sin 195° given sin 195°=sin (225°-30°)

Basically what I need to know is how sin 225° = -sin 45°....how do I know that sin 225° is equal to -sin 45°?

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you can multiply

Quote:

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Originally Posted by Ericonda

how do I know that sin 225° is equal to -sin 45°?

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Hello,

Because 225°=180+45

And if you look at a unit circle, sin(180+x)=-sin(x) ;)