... l o 20 12 2 011 20 10 20 09 20 12 20 12 C2012C20 12 C2012C20 12 + C2012C20 12 C2012C20 12 + + C20 12 C20 12 +) Ta cú ( x ) 20 12 ( + x ) 20 12 0,5 2 011 20 12 = ( C20 12 ) ( C20 12 ) + ( C20 12 ) ( C20 12 ) ... ) 20 12 20 12 = ( x2 ) k = C20 12 ( x ) k =0 k 0 ,25 0 ,25 0,5 0,5 0,5 20 12 0,5 1006 suy h s ca s hng cha x 20 12 l C20 12 0,5 20 12 20 12 k k k = C20 12 ( x ) ữ C20 12 x k ữ k =0 k = 20 12 ... Bi cos (2 B + 2C ) + 2( cos2 B + cos2C ) + sin 2 B sin 2C cos 2 B cos 2C + sin B sin 2C + + + + cos2 Bcos2C + 2( cos2 B + cos2C ) = 2 2 2 sin B sin 2C cos2B cos2C + + 1ữ = ữ + 2 2 Du...