3-2x(2x+5)=-20

Solution for 3-2x(2x+5)=-20 equation:

3-2x(2x+5)=-20

We move all terms to the left:

3-2x(2x+5)-(-20)=0

We add all the numbers together, and all the variables

-2x(2x+5)+23=0

We multiply parentheses

-4x^2-10x+23=0

a = -4; b = -10; c = +23;
Δ = b2-4ac
Δ = -102-4·(-4)·23
Δ = 468
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:

$\sqrt{\Delta}=\sqrt{468}=\sqrt{36*13}=\sqrt{36}*\sqrt{13}=6\sqrt{13}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-6\sqrt{13}}{2*-4}=\frac{10-6\sqrt{13}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+6\sqrt{13}}{2*-4}=\frac{10+6\sqrt{13}}{-8}
$