Помогите, пожалуйста с №1,3,4

1. а) $sin70^0+sin50^0=2sin \frac{ 70^0 + 50^0 }{2} cos \frac{70^0 - 50^0 }{2} =2sin60^0cos10^0$
б) $sin70^0-sin50^0=2sin \frac{70^0-50^0}{2} cos\frac{70^0+50^0}{2}=2sin10^0cos60^0$
в) $cos70^0+cos50^0=2cos \frac{70^0-50^0}{2}cos \frac{70^0+50^0}{2}=2cos10^0cos60^0$
г) $cos70^0-cos50^0=-2sin \frac{70^0+50^0}{2}sin \frac{70^0-50^0}{2} =-2sin60^0sin10^0$
2. $sin200^0+sin100^0=sin40^0$
$sin200^0+sin100^0=2sin \frac{200^0+100^0}{2} cos \frac{200^0-100^0}{2}=2sin150^0cos50^0=$ $2sin(180^0-30^0)cos(90^0-40^0)=2sin30^0sin40^0=2* \frac{1}{2} sin40^0$ $=sin40^0$
$sin40^0=sin40^0$
3. $sin \frac{7 \pi }{12} +sin \frac{ \pi }{12} +cos \frac{ \pi }{12} -cos \frac{7 \pi }{12} =2sin \frac{ \frac{7 \pi }{12} + \frac{ \pi }{12} }{2} cos \frac{ \frac{7 \pi }{12} - \frac{ \pi }{12} }{2} =2sin \frac{ \pi }{3} cos \frac{ \pi }{4} =$ $2* \frac{ \sqrt{3} }{2} * \frac{ \sqrt{2} }{2} =\frac{ \sqrt{6} }{2}$
4. $sin13^0+sin15^0+sin17^0=(sin13^0+sin17^0)+sin15^0=$ $2sin \frac{17^0+13^0}{2}cos \frac{17^0-13^0}{2} +sin15^0=2sin15^0cos2^0+sin15^0=$ $sin15^0(2cos2^0+1)$