Question

При каких значениях x трехчлен x2 + 1,8x – 0,6 принимает значение m = 3?
Ответ: x1 = х2=​

Answer 1

Ответ:

$\displaystyle \: x _{1} = - 3 \\ x _{2} = 1.2$

Объяснение:

${x}^{2} + 1.8x - 0.6 = m \\ {x}^{2} + 1.8x - 0.6 = 3 \\ {x }^{2} + 1.8x - 0.6 - 3 = 0 \\ {x}^{2} + 1.8x - 3.6 = 0 \: | \times 5 \\ 5 {x}^{2} + 9x - 18 = 0 \\ D = {b}^{2} - 4ac = {9}^{2} - 4 \times 5 \times ( - 18) = 81 + 360 = 441 = {21}^{2} \\ x _{1 \: 2} = \frac{ - b \pm \sqrt{D} }{2a} = \frac{ - 9 \pm 21 }{2 \times 5} = \frac{ - 9 \pm21}{10} \\ x _{1} = \frac{ - 9 - 21}{10} = \frac{ - 30}{10} = -3 \\ x _{2} = \frac{ - 9 + 21}{2} = \frac{12}{10} = \frac{6}{5} = 1.2$