lets solve the quadratic equation:
7x^2 + 2x = 0
(x)(7x + 2) = 0
therefore, for this equation to hold we need, either one of these conditions:
x = 0
or
7x + 2 = 0
from where:
7x = -2
x = -2/7
then, we have two solutions for the equation as expected being quadratic.
