Angle a, b and c have a sum of 180 degrees. Prove that Sina +sinb - siny = y/2 * sinb/2 * cosc/2 can you help me with these (without the last one). Need them in a couple days

Angle a b and c have a sum of 180 degrees Prove that Sina sinb siny y2 sinb2 cosc2 can you help me with these without the last one Need them in a couple days class=