B) x²+3x = 10-x-3x²+8x 5 2 14 ;

в) $$\frac{x^2+3x}{5} = \frac{10-x}{2} - \frac{3x^2+8x}{14}$$

Умножим обе части уравнения на 70:

$$14(x^2+3x) = 35(10-x) - 5(3x^2+8x)$$

$$14x^2+42x = 350-35x - 15x^2-40x$$

$$14x^2+42x - 350+35x + 15x^2+40x= 0$$

$$29x^2+117x-350= 0$$

$$D = (117)^2 - 4 \cdot 29 \cdot (-350) = 13689 + 40600 = 54289 = 233^2$$

$$x_1 = \frac{-117 + \sqrt{54289}}{2 \cdot 29} = \frac{-117+233}{58} = \frac{116}{58} = 2$$

$$x_2 = \frac{-117 - \sqrt{54289}}{2 \cdot 29} = \frac{-117-233}{58} = \frac{-350}{58} = -\frac{175}{29}$$

Ответ: $$x=2; x=-\frac{175}{29}$$