21x^2+16x-16=0

Solution for 21x^2+16x-16=0 equation:

21x^2+16x-16=0

a = 21; b = 16; c = -16;
Δ = b2-4ac
Δ = 162-4·21·(-16)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-40}{2*21}=\frac{-56}{42}
=-1+1/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+40}{2*21}=\frac{24}{42}
=4/7
$