1. 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°?

2. 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°?
$sin(225-30)=\sin(225)cos(30)-cos(225)sin(30)=\frac{-\sqrt{2}}{2}\frac{\sqrt{3}}{2}-\frac{-\sqrt{2}}{2}\frac{1}{2}$
you can multiply

3. Originally Posted by Ericonda
how do I know that sin 225° is equal to -sin 45°?
Hello,

Because 225°=180+45

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