\left. \begin{array} { c } { \text { If } \angle A + \angle B + \angle C = 180 ^ { \circ } \text { then, prove that: } } \\ { \operatorname { sin } A + \operatorname { sin } B - \operatorname { sin } C = 4 \operatorname { sin } \frac { A } { 2 } \operatorname { sin } \frac { B } { 2 } \operatorname { cos } \frac { C } { 2 } } \end{array} \right.

\left. \begin{array} { c } { \text { If } \angle A + \angle B + \angle

1.	\left. \begin{array} { c } { \text { If } \angle A + \angle B + \angle C = 180 ^ { \circ } \text { then, prove that: } } \\ { \operatorname { sin } A + \operatorname { sin } B - \operatorname { sin } C = 4 \operatorname { sin } \frac { A } { 2 } \operatorname { sin } \frac { B } { 2 } \operatorname { cos } \frac { C } { 2 } } \end{array} \right.
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