x2+16x-21=0

Solution for x2+16x-21=0 equation:

x2+16x-21=0

We add all the numbers together, and all the variables

x^2+16x-21=0

a = 1; b = 16; c = -21;
Δ = b2-4ac
Δ = 162-4·1·(-21)
Δ = 340
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:

$\sqrt{\Delta}=\sqrt{340}=\sqrt{4*85}=\sqrt{4}*\sqrt{85}=2\sqrt{85}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-2\sqrt{85}}{2*1}=\frac{-16-2\sqrt{85}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+2\sqrt{85}}{2*1}=\frac{-16+2\sqrt{85}}{2}
$