Решите уравнение (2a²-5a)+12a-30=0

Решите задачу:

$(2 {a}^{2} - 5a) + 12a - 30 = 0 \\ 2 {a}^{2} - 5a + 12a - 30 = 0 \\ 2 {a}^{2} + 7a - 30 = 0 \\ d = b ^{2} - 4ac = {7}^{2} - 4 \times 2 \times ( - 30) = 49 + 240 = 289 \\ a1 = \frac{ - b + \sqrt{d} }{2a} = \frac{ - 7 + \sqrt{289} }{2 \times 2} = \frac{ - 7 + 17}{4} = \frac{10}{4} = \frac{5}{2} = 2 \frac{1}{2} = 2.5 \\ a2 = \frac{ - b - \sqrt{d} }{2a} = \frac{ - 7 - 17}{4} = \frac{ - 24}{4} = - 6$