40=(x+2)(x-1)

Solution for 40=(x+2)(x-1) equation:

40=(x+2)(x-1)

We move all terms to the left:

40-((x+2)(x-1))=0

We multiply parentheses ..

-((+x^2-1x+2x-2))+40=0


We calculate terms in parentheses: -((+x^2-1x+2x-2)), so:

(+x^2-1x+2x-2)

We get rid of parentheses

x^2-1x+2x-2

We add all the numbers together, and all the variables

x^2+x-2

Back to the equation:

-(x^2+x-2)


We get rid of parentheses

-x^2-x+2+40=0

We add all the numbers together, and all the variables

-1x^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
$