Cosa+cosb если a+b=180°

Question

Cosa+cosb если a+b=180°

Answer 1

2сos a+b/2 *cos(a-b/2)
2cos180°/2 *cos(a-b/2)
2cos90°*cos(a-b/2)
Т. к. cos90°=0, то 2сos90°*сos( a-b/2)=0