Question

[oOo Min min oOo]

CMR trong mọi tam giác ABC

a) r + r_a + r_{b - r = 4R.cosC}

_b)tan\(\frac{B}{2}\). tan \(\frac{C}{2}\) = \(\frac{h_a-2r}{h_a}\) = \(\frac{h_a}{2r_a+h_a}\)

c) cos\(\frac{A}{2}\) = \(\sqrt{\frac{p\left(p-a\right)}{bc}}\) ; tan\(\frac{A}{2}\) = \(\sqrt{\frac{\left(p-b\right)\left(p-c\right)}{p\left(p-a\right)}}\)