-3x(x-14)=42

Solution for -3x(x-14)=42 equation:

-3x(x-14)=42

We move all terms to the left:

-3x(x-14)-(42)=0

We multiply parentheses

-3x^2+42x-42=0

a = -3; b = 42; c = -42;
Δ = b2-4ac
Δ = 422-4·(-3)·(-42)
Δ = 1260
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1260}=\sqrt{36*35}=\sqrt{36}*\sqrt{35}=6\sqrt{35}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(42)-6\sqrt{35}}{2*-3}=\frac{-42-6\sqrt{35}}{-6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(42)+6\sqrt{35}}{2*-3}=\frac{-42+6\sqrt{35}}{-6}
$