Question

(2x-1)(2x+3)-(x-2)(x+2)=21 розв'яжіть рівняння​

Answer 1

Ответ:

$(2x - 1)(2x + 3) - (x - 2)(x + 2) = 21 \\ 4 {x}^{2} + 6x - 2x - 3 - ( {x}^{2} - 4) = 21 \\ 4 {x}^{2} + 4x - 3 - {x}^{2} + 4 = 21 \\3 {x}^{2} + 4x - 20 = 0 \\ d = {4}^{2} - 4 \times 3 \times ( - 20) = 16 + 240 = 256 = {16}^{2} \\ x1 = \frac{ - 4 - 16}{6} = \frac{ - 20}{6} = \frac{ - 10}{3} \\ x2 = \frac{ - 4 + 16}{6} = \frac{12}{6} = 2$