15x2-x-28=0

Solution for 15x2-x-28=0 equation:

15x^2-x-28=0

We add all the numbers together, and all the variables

15x^2-1x-28=0

a = 15; b = -1; c = -28;
Δ = b2-4ac
Δ = -12-4·15·(-28)
Δ = 1681
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1681}=41$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-41}{2*15}=\frac{-40}{30}
=-1+1/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+41}{2*15}=\frac{42}{30}
=1+2/5
$