A=(29,7-2x)(21-2x)+2(29,7-2x)x+2(21-2x)x

Solution for A=(29,7-2x)(21-2x)+2(29,7-2x)x+2(21-2x)x equation:

=(29.7-2A)(21-2A)+2(29.7-2A)A+2(21-2A)A

We move all terms to the left:

-((29.7-2A)(21-2A)+2(29.7-2A)A+2(21-2A)A)=0

We add all the numbers together, and all the variables

-((-2A+29.7)(-2A+21)+2(-2A+29.7)A+2(-2A+21)A)=0

We multiply parentheses ..

-((+4A^2-42A-59.4A+623.7)+2(-2A+29.7)A+2(-2A+21)A)=0


We calculate terms in parentheses: -((+4A^2-42A-59.4A+623.7)+2(-2A+29.7)A+2(-2A+21)A), so:

(+4A^2-42A-59.4A+623.7)+2(-2A+29.7)A+2(-2A+21)A

We multiply parentheses

(+4A^2-42A-59.4A+623.7)-4A^2-4A^2+59.4A+42A

We get rid of parentheses

4A^2-4A^2-4A^2-42A-59.4A+59.4A+42A+623.7

We add all the numbers together, and all the variables

-4A^2-15A+623.7-7.105427357601E

We add all the numbers together, and all the variables

-4A^2-15A+604.3854459304

Back to the equation:

-(-4A^2-15A+604.3854459304)


We get rid of parentheses

4A^2+15A-604.3854459304=0

a = 4; b = 15; c = -604.3854459304;
Δ = b2-4ac
Δ = 152-4·4·(-604.3854459304)
Δ = 9895.1671348864
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-\sqrt{9895.1671348864}}{2*4}=\frac{-15-\sqrt{9895.1671348864}}{8}
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+\sqrt{9895.1671348864}}{2*4}=\frac{-15+\sqrt{9895.1671348864}}{8}
$