... (x +y+ z)x+x2]- (y+ z)( y 2-yz+z2)= (y+ z)[( x +y+ z)2 + (x +y+ z)x+x2]- (y+ z)( y 2-yz+z2)= (y+ z)( x2 +y 2+z2 +2xy+2xz +2yz +x2+xy+xz+x2 -y 2+yz-z2) 0,5đ= (y+ z)( 3x2+3xy+3xz +3yz)= (y+ z)( ... +4 + 1 0,5đ= (x2- 2xy +y 2)+ (y 2- 4y +4) + 1 = (x -y) 2 + (y - 2)2 + 1 0,5đDo (x -y) 2 0 ; (y - 2)2 0 0,5đNên B = (x -y) 2 + (y - 2)2 + 1 1 Khi x = y v y = 2 thì B =1 V y giá ... 3x2+3xy+3xz +3yz) 0,5đ= 3 (y+ z)[(x2+xy)+(xz +yz)]= 3 (y+ z)[x(x +y) +z(x +y) ]= 3 (x +y) (y+ z)(x +z) 0,5đBài 4: (2đ) B = x2-2xy+ 2y 2- 4y+ 5Tách các số hạng ta đợc:B = x2- 2xy +y 2 +y 2- 4y +4...