Question

B) 4x² - 4x - 3=0;
Г) 4x² - 4x - 15 = 0.

Answer 1

в)

$4 {x}^{2} - 4x - 3 = 0 \\ d = ( - 4) {}^{2} - 4 \times 4 \times ( - 3) = \\ 16 + 48 = 64 \\ x_{1} = \frac{4 + 8}{4 \times 2} = \frac{12}{4 \times 2} = \frac{3}{2} = 1.5 \\ x _{2} = \frac{4 - 8}{4 \times 2} = - \frac{4}{4 \times 2} = - \frac{1}{2} = - 0.5$

г)

$4 {x}^{2} - 4x - 15 = 0 \\ d = ( - 4) {}^{2} - 4 \times 4 \times ( - 15) = \\ 16 + 240 = 256 \\ x_{1} = \frac{4 + 16}{4 \times 2} = \frac{20}{4 \times 2} = \frac{5}{2} = 2.5 \\ x _{2} = \frac{4 - 16}{4 \times 2} = - \frac{12}{4 \times2 } = - \frac{3}{2} = - 1.5$