Thu gọn lại 3 câu trong đề

`1. text{M}=(sinA.cosB)/(sin(B+C))-(3cos(B+C))/(cosA)`

`text{M}=(sinA.cosB)/(sin(180^@-A))-(3cos(180^@-A))/(cosA)`

`text{M}=(sinA.cosB)/(sinA)-(-3cosA)/(cosA)`

`text{M}=cosB+3`

Vậy `text{M}=cosB+3`

`2. text{M}=(tanB/2.cos(A+C)/2.cosA)/(cot((A+C)/2).sinB/2)`

`text{M}=((sinB/2)/(cosB/2).cos(A+C)/2.cosA)/((cos((A+C)/2))/(sin((A+C)/2)).sinB/2)`

`text{M}=((1)/(cosB/2).cosA)/(sin((A+C)/2))`

`text{M}=(cosA)/(cosB/2.sin((A+C)/2)`

Vậy `text{M}=(cosA)/(cosB/2.sin((A+C)/2)`

`3. text{M}=sin^2((A+B)/2)-cos^2(C/2).tan(A+B).cotC`

`text{M}=sin^2((180^@-C)/2)-cos^2(C/2).tan(180^@-C). 1/tanC`

`text{M}=sin^2(90^@-(C)/2)-cos^2(C/2).(-tanC). 1/tanC`

`text{M}=cos^2(C/2)+cos^2(C/2)`

`text{M}=2cos^2(C/2)`

Vậy `text{M}=2cos^2(C/2)`