2.1*3.7=(15-x)x

Solution for 2.1*3.7=(15-x)x equation:

2.1*3.7=(15-x)x

We move all terms to the left:

2.1*3.7-((15-x)x)=0

We add all the numbers together, and all the variables

-((-1x+15)x)+2.1*3.7=0

We add all the numbers together, and all the variables

-((-1x+15)x)+7.77=0


We calculate terms in parentheses: -((-1x+15)x), so:

(-1x+15)x

We multiply parentheses

-1x^2+15x

Back to the equation:

-(-1x^2+15x)


We get rid of parentheses

1x^2-15x+7.77=0

We add all the numbers together, and all the variables

x^2-15x+7.77=0

a = 1; b = -15; c = +7.77;
Δ = b2-4ac
Δ = -152-4·1·7.77
Δ = 193.92
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-\sqrt{193.92}}{2*1}=\frac{15-\sqrt{193.92}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{193.92}}{2*1}=\frac{15+\sqrt{193.92}}{2}
$