1)5x^2-8x+3=0 2)-2x^2+x+15=0 3)3x^2+x-30=0 Через дискриминант.

Объяснение:

1) 5х²- 8х+3=0

D= 64-4×3×5= 4

D= +-2

$x1 = \frac{8 + 2}{5 \times 2} = 1$

$x2 = \frac{8 - 2}{5 \times 2} = \frac{3}{5} = 0.6$

2) -2x²+x+15=0

2x²-x-15= 0

D= 1- 4×2×(-15)= 121

D= +-11

$x1 = \frac{ - 1 + 11}{ 2 \times 2} = \frac{5}{2} = 2.5$

$x2 = \frac{ - 1 - 11}{2 \times 2} = - 3$

3) 3x²+x-30=0

D= 1×4×3×(-30)= 361

D= +-19

$x1 = \frac{ - 1 + 19}{3 \times 2} = 3$

$x2 = \frac{ - 1 - 19}{3 \times 2} = - \frac{20}{3} = - 6 \frac{2}{3}$