-5(x)=x^2+3x-21

Solution for -5(x)=x^2+3x-21 equation:

-5(x)=x^2+3x-21

We move all terms to the left:

-5(x)-(x^2+3x-21)=0

We get rid of parentheses

-x^2-5x-3x+21=0

We add all the numbers together, and all the variables

-1x^2-8x+21=0

a = -1; b = -8; c = +21;
Δ = b2-4ac
Δ = -82-4·(-1)·21
Δ = 148
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:

$\sqrt{\Delta}=\sqrt{148}=\sqrt{4*37}=\sqrt{4}*\sqrt{37}=2\sqrt{37}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-2\sqrt{37}}{2*-1}=\frac{8-2\sqrt{37}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+2\sqrt{37}}{2*-1}=\frac{8+2\sqrt{37}}{-2}
$