140x=5x*4x

Solution for 140x=5x*4x equation:

140x=5x*4x

We move all terms to the left:

140x-(5x*4x)=0

We add all the numbers together, and all the variables

140x-(+5x*4x)=0

We get rid of parentheses

140x-5x*4x=0

Wy multiply elements

-20x^2+140x=0

a = -20; b = 140; c = 0;
Δ = b2-4ac
Δ = 1402-4·(-20)·0
Δ = 19600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{19600}=140$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(140)-140}{2*-20}=\frac{-280}{-40}
=+7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(140)+140}{2*-20}=\frac{0}{-40}
=0
$