Given the equation:
$$5 x^{4} + 2 x^{3} = 0$$
transform
Take common factor x^2 from the equation
we get:
$$x^{2} \left(5 x^{2} + 2 x\right) = 0$$
then:
$$x_{1} = 0$$
and also
we get the equation
$$5 x^{2} + 2 x = 0$$
This equation is of the form
a*x^2 + b*x + c = 0
A quadratic equation can be solved
using the discriminant.
The roots of the quadratic equation:
$$x_{2} = \frac{\sqrt{D} - b}{2 a}$$
$$x_{3} = \frac{- \sqrt{D} - b}{2 a}$$
where D = b^2 - 4*a*c - it is the discriminant.
Because
$$a = 5$$
$$b = 2$$
$$c = 0$$
, then
D = b^2 - 4 * a * c =
(2)^2 - 4 * (5) * (0) = 4
Because D > 0, then the equation has two roots.
x2 = (-b + sqrt(D)) / (2*a)
x3 = (-b - sqrt(D)) / (2*a)
or
$$x_{2} = 0$$
$$x_{3} = - \frac{2}{5}$$
The final answer for 5*x^4 + 2*x^3 = 0:
$$x_{1} = 0$$
$$x_{2} = 0$$
$$x_{3} = - \frac{2}{5}$$