9x-x=4x+7x^2

Solution for 9x-x=4x+7x^2 equation:

9x-x=4x+7x^2

We move all terms to the left:

9x-x-(4x+7x^2)=0

We add all the numbers together, and all the variables

-(4x+7x^2)+8x=0

We get rid of parentheses

-7x^2-4x+8x=0

We add all the numbers together, and all the variables

-7x^2+4x=0

a = -7; b = 4; c = 0;
Δ = b2-4ac
Δ = 42-4·(-7)·0
Δ = 16
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{16}=4$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-4}{2*-7}=\frac{-8}{-14}
=4/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+4}{2*-7}=\frac{0}{-14}
=0
$