(20-2x)(21-2x)=210

Solution for (20-2x)(21-2x)=210 equation:

(20-2x)(21-2x)=210

We move all terms to the left:

(20-2x)(21-2x)-(210)=0

We add all the numbers together, and all the variables

(-2x+20)(-2x+21)-210=0

We multiply parentheses ..

(+4x^2-42x-40x+420)-210=0

We get rid of parentheses

4x^2-42x-40x+420-210=0

We add all the numbers together, and all the variables

4x^2-82x+210=0

a = 4; b = -82; c = +210;
Δ = b2-4ac
Δ = -822-4·4·210
Δ = 3364
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3364}=58$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-82)-58}{2*4}=\frac{24}{8}
=3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-82)+58}{2*4}=\frac{140}{8}
=17+1/2
$