0=x^2+15x-26

Solution for 0=x^2+15x-26 equation:

0=x^2+15x-26

We move all terms to the left:

0-(x^2+15x-26)=0

We add all the numbers together, and all the variables

-(x^2+15x-26)=0

We get rid of parentheses

-x^2-15x+26=0

We add all the numbers together, and all the variables

-1x^2-15x+26=0

a = -1; b = -15; c = +26;
Δ = b2-4ac
Δ = -152-4·(-1)·26
Δ = 329
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-\sqrt{329}}{2*-1}=\frac{15-\sqrt{329}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{329}}{2*-1}=\frac{15+\sqrt{329}}{-2}
$