-14x^2+7x+21=0

Solution for -14x^2+7x+21=0 equation:

-14x^2+7x+21=0

a = -14; b = 7; c = +21;
Δ = b2-4ac
Δ = 72-4·(-14)·21
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(7)-35}{2*-14}=\frac{-42}{-28}
=1+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+35}{2*-14}=\frac{28}{-28}
=-1
$