SIN A . COS B= 12 (SIN (A −B)+SIN ( A+B)) 4. COS A . SIN B= 12 (SIN...

3. sin a . cos b= 1

2 (sin (a −b)+sin ( a+b)) 4. cos a . sin b= 1

2 (sin( a+ b) −sin (a −b))

VIII. HAI GểC ĐỐI NHAU