56x+2.1x^2=1000

Solution for 56x+2.1x^2=1000 equation:

56x+2.1x^2=1000

We move all terms to the left:

56x+2.1x^2-(1000)=0

a = 2.1; b = 56; c = -1000;
Δ = b2-4ac
Δ = 562-4·2.1·(-1000)
Δ = 11536
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:

$\sqrt{\Delta}=\sqrt{11536}=\sqrt{16*721}=\sqrt{16}*\sqrt{721}=4\sqrt{721}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(56)-4\sqrt{721}}{2*2.1}=\frac{-56-4\sqrt{721}}{4.2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(56)+4\sqrt{721}}{2*2.1}=\frac{-56+4\sqrt{721}}{4.2}
$