1400=(40-2x)(70-2x)

Solution for 1400=(40-2x)(70-2x) equation:

1400=(40-2x)(70-2x)

We move all terms to the left:

1400-((40-2x)(70-2x))=0

We add all the numbers together, and all the variables

-((-2x+40)(-2x+70))+1400=0

We multiply parentheses ..

-((+4x^2-140x-80x+2800))+1400=0


We calculate terms in parentheses: -((+4x^2-140x-80x+2800)), so:

(+4x^2-140x-80x+2800)

We get rid of parentheses

4x^2-140x-80x+2800

We add all the numbers together, and all the variables

4x^2-220x+2800

Back to the equation:

-(4x^2-220x+2800)


We get rid of parentheses

-4x^2+220x-2800+1400=0

We add all the numbers together, and all the variables

-4x^2+220x-1400=0

a = -4; b = 220; c = -1400;
Δ = b2-4ac
Δ = 2202-4·(-4)·(-1400)
Δ = 26000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{26000}=\sqrt{400*65}=\sqrt{400}*\sqrt{65}=20\sqrt{65}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(220)-20\sqrt{65}}{2*-4}=\frac{-220-20\sqrt{65}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(220)+20\sqrt{65}}{2*-4}=\frac{-220+20\sqrt{65}}{-8}
$