... sau: a) 7x2 - 9x + = 0; b) 23x2 - 9x - 32 = Gii a) 7x2 - 9x + = (a = 7; b = -9; c = 2) Vỡ a + b + c = + ( -9) + = nờn PT cú nghim x1 = v x2 = c = a b) 23x2 - 9x - 32 = (a = 23; b = -9; c = -32) ... b) x2 - 49x - 50 = Gii: a) 2x2 5x + = (a = 2; b = -5; c = 3) Vỡ a + b + c = + (-5) + = nờn PT cú nghim x1 = v x2 = c = a b) x2 - 49x - 50 = (a = 1; b = - 49; c = -50) Vỡ a - b + c = (- 49) + (-50) ... hai : a) 5x2 - 3x - = cú a = 5, b = - 3, c = - b) 7x2 - = cú a = 7, b = 0, c = -7 c) 9x - 9x = cú a = 9, b = -9, c = Mt s vớ d v gii phng trỡnh bc hai cú h s b = hoc c = * Trng hp c = 0, phng trỡnh...