x2+8x=9x+42

Solution for x2+8x=9x+42 equation:

x2+8x=9x+42

We move all terms to the left:

x2+8x-(9x+42)=0

We add all the numbers together, and all the variables

x^2+8x-(9x+42)=0

We get rid of parentheses

x^2+8x-9x-42=0

We add all the numbers together, and all the variables

x^2-1x-42=0

a = 1; b = -1; c = -42;
Δ = b2-4ac
Δ = -12-4·1·(-42)
Δ = 169
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{169}=13$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-13}{2*1}=\frac{-12}{2}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+13}{2*1}=\frac{14}{2}
=7
$