104=(15-x)*(10-x)

Solution for 104=(15-x)*(10-x) equation:

104=(15-x)(10-x)

We move all terms to the left:

104-((15-x)(10-x))=0

We add all the numbers together, and all the variables

-((-1x+15)(-1x+10))+104=0

We multiply parentheses ..

-((+x^2-10x-15x+150))+104=0


We calculate terms in parentheses: -((+x^2-10x-15x+150)), so:

(+x^2-10x-15x+150)

We get rid of parentheses

x^2-10x-15x+150

We add all the numbers together, and all the variables

x^2-25x+150

Back to the equation:

-(x^2-25x+150)


We get rid of parentheses

-x^2+25x-150+104=0

We add all the numbers together, and all the variables

-1x^2+25x-46=0

a = -1; b = 25; c = -46;
Δ = b2-4ac
Δ = 252-4·(-1)·(-46)
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(25)-21}{2*-1}=\frac{-46}{-2}
=+23
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(25)+21}{2*-1}=\frac{-4}{-2}
=+2
$