Friday, April 10, 2015

What is the solution of the equation x^3+3x^2+4x+2=0, if it is integer?

We'll re-write the equation, keeping the first 3 terms to the
left side. For this teason, we'll move 2 to the right
side:


x^3+3x^2+4x = -2


We'll factorize
by x to the left side:


x(x^2 + 3x + 4) =
-2


If the solution of the equation is an integer number,x, it has to
divide -2, as well.


We'll identify the divisors of
-2:


D = -2 ; -1 ; 1 ; 2


We'll
substitute the divisor into equation.


For x =
-1


-1*[(-1)^2 + 3(-1) + 4] =
-2


-1*(4-2) = -2


-2 =
-2


x = -1 is the solution of the
equation.


We'll put x = -2:


-2*[(-2)^2
+ 3(-2) + 4] = -2


-2(4 - 6 + 4) =
-2


-2*2 = -2


-4 = -2
impossible!


x = -2 is not a solution for the
equation!


We'll put x = 1


1*[(1)^2 +
3*(1) + 4] = -2


8 = -2 impossible


x =
2


2*[(2)^2 + 3*(2) + 4] = -2


28 = -2
impossible


We notice that for positive values of x, the expression
has values bigger than -2.


The only integer solution
for the equation is x = -1.

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