(X+1)(x-2)=3x

Solution for (X+1)(x-2)=3x equation:

(X+1)(X-2)=3X

We move all terms to the left:

(X+1)(X-2)-(3X)=0

We add all the numbers together, and all the variables

-3X+(X+1)(X-2)=0

We multiply parentheses ..

(+X^2-2X+X-2)-3X=0

We get rid of parentheses

X^2-2X+X-3X-2=0

We add all the numbers together, and all the variables

X^2-4X-2=0

a = 1; b = -4; c = -2;
Δ = b2-4ac
Δ = -42-4·1·(-2)
Δ = 24
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:

$\sqrt{\Delta}=\sqrt{24}=\sqrt{4*6}=\sqrt{4}*\sqrt{6}=2\sqrt{6}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{6}}{2*1}=\frac{4-2\sqrt{6}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{6}}{2*1}=\frac{4+2\sqrt{6}}{2}
$