A=x(70-2x)

Solution for A=x(70-2x) equation:

=A(70-2A)

We move all terms to the left:

-(A(70-2A))=0

We add all the numbers together, and all the variables

-(A(-2A+70))=0


We calculate terms in parentheses: -(A(-2A+70)), so:

A(-2A+70)

We multiply parentheses

-2A^2+70A

Back to the equation:

-(-2A^2+70A)


We get rid of parentheses

2A^2-70A=0

a = 2; b = -70; c = 0;
Δ = b2-4ac
Δ = -702-4·2·0
Δ = 4900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4900}=70$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-70)-70}{2*2}=\frac{0}{4}
=0
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-70)+70}{2*2}=\frac{140}{4}
=35
$