21x2-84x+15x-60=0

Solution for 21x2-84x+15x-60=0 equation:

21x^2-84x+15x-60=0

We add all the numbers together, and all the variables

21x^2-69x-60=0

a = 21; b = -69; c = -60;
Δ = b2-4ac
Δ = -692-4·21·(-60)
Δ = 9801
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9801}=99$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-69)-99}{2*21}=\frac{-30}{42}
=-5/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-69)+99}{2*21}=\frac{168}{42}
=4
$