Question

15х2+2х-8=0

В Ответ записать значение выражения 3х1-5х2

Answer 1

$15 {x}^{2} + 2x - 8 = 0 \\ D = {2}^{2} - 4 \times 15 \times ( -8 ) = \\ = 4 + 320 = 324 = {18}^{2} \\ x_½ = \frac{ - 2±18}{2 \times 15} \\ x_1 = - \frac{2}{3} \: \: \: \: \: x_2 = \frac{8}{15} \\ \\ 3 \times x_1 - 5 \times x_2 = \\ = 3 \times ( - \frac{2}{3} ) - 5 \times \frac{8}{15} = \\ = - 2 - \frac{8}{3} = - 4 \frac{2}{3}$