Решите пожалуйста 21,22,23

21) x^{2} - 3x +  \sqrt{6-x} =  \sqrt{6-x} + 40 x^{2} - 3x +  \sqrt{6-x} - \sqrt{6-x} - 40 = 0 x^{2} - 3x - 40 = 0 D = 3^{2} - 4 * 1 * -40 = 9 + 160 = 169; \sqrt{D} = 13; x1 = (3 + 13) / 2 = 8; x2 = (3 - 13) / 2 = -5; 22) x - 1 = (x + 7) * (2/3) x - x*2/3 = 7*2/3 +1 x = (7*2/3 + 1) * 3 x = 14 + 3 = 17км/ч