X^2+16x-21=-5

Solution for X^2+16x-21=-5 equation:

X^2+16X-21=-5

We move all terms to the left:

X^2+16X-21-(-5)=0

We add all the numbers together, and all the variables

X^2+16X-16=0

a = 1; b = 16; c = -16;
Δ = b2-4ac
Δ = 162-4·1·(-16)
Δ = 320
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:

$\sqrt{\Delta}=\sqrt{320}=\sqrt{64*5}=\sqrt{64}*\sqrt{5}=8\sqrt{5}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-8\sqrt{5}}{2*1}=\frac{-16-8\sqrt{5}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+8\sqrt{5}}{2*1}=\frac{-16+8\sqrt{5}}{2}
$