3x(x+5)-11=7

Solution for 3x(x+5)-11=7 equation:

3x(x+5)-11=7

We move all terms to the left:

3x(x+5)-11-(7)=0

We add all the numbers together, and all the variables

3x(x+5)-18=0

We multiply parentheses

3x^2+15x-18=0

a = 3; b = 15; c = -18;
Δ = b2-4ac
Δ = 152-4·3·(-18)
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-21}{2*3}=\frac{-36}{6}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+21}{2*3}=\frac{6}{6}
=1
$