cho tam giác ABC , chứng minh rằng :
a) \(\sin\)(B + C) = \(\sin\)A
b) \(\cos\)(A + B) = -\(\cos\)C
c) \(\sin\)\(\frac{B+C}{2}\) = \(\cos\)\(\frac{A}{2}\)
d) \(\tan\)\(\frac{A+C}{2}\) = \(\cot\) \(\frac{B}{2}\)
Loga
Toán lớp 10
