... x, y, z a x y2 z2 xy b x y2 z2 2( x Cho x y z yz : zx y z) x2 y g minh rng z 3.1.2 y2 z x z2 x y x2 y2 z2 X , tng ng vi c chng minh ỳng y x y 1 + + x+ z x z y z 1 + x z x+ z (1) Li gii (1) x ... ab 0 iu phi chng minh , b ta luụn a+ b 1+ a+ b a+ b 1+ a + b Li gii - K33D SP a b a b : a a b (1 b a a b b) a b a b a a b a (a b )(1 a b b a b) a b a b a a b b b õy iu phi chng minh C khụ C (1+ ... + sin2B + sin2C + cos2A+ cos2B+ cos2C + sin2A sin2B sin2C >4 Vy bt ng thc c chng minh BsinC cosA iu phi chng minh - K33D SP rng: Cho a, b, c b a a2 + b2 + c2 ab bc ca b (ab+bc+ca)2 3abc(a b...