-7a(a-21)=14

Solution for -7a(a-21)=14 equation:

-7a(a-21)=14

We move all terms to the left:

-7a(a-21)-(14)=0

We multiply parentheses

-7a^2+147a-14=0

a = -7; b = 147; c = -14;
Δ = b2-4ac
Δ = 1472-4·(-7)·(-14)
Δ = 21217
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{21217}=\sqrt{49*433}=\sqrt{49}*\sqrt{433}=7\sqrt{433}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(147)-7\sqrt{433}}{2*-7}=\frac{-147-7\sqrt{433}}{-14}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(147)+7\sqrt{433}}{2*-7}=\frac{-147+7\sqrt{433}}{-14}
$