21z2+85z-26=0

Solution for 21z2+85z-26=0 equation:

21z^2+85z-26=0

a = 21; b = 85; c = -26;
Δ = b2-4ac
Δ = 852-4·21·(-26)
Δ = 9409
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9409}=97$
$z_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(85)-97}{2*21}=\frac{-182}{42}
=-4+1/3
$
$z_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(85)+97}{2*21}=\frac{12}{42}
=2/7
$