3x(x-4)=7

Solution for 3x(x-4)=7 equation:

3x(x-4)=7

We move all terms to the left:

3x(x-4)-(7)=0

We multiply parentheses

3x^2-12x-7=0

a = 3; b = -12; c = -7;
Δ = b2-4ac
Δ = -122-4·3·(-7)
Δ = 228
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:

$\sqrt{\Delta}=\sqrt{228}=\sqrt{4*57}=\sqrt{4}*\sqrt{57}=2\sqrt{57}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-2\sqrt{57}}{2*3}=\frac{12-2\sqrt{57}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+2\sqrt{57}}{2*3}=\frac{12+2\sqrt{57}}{6}
$