Solve the equation

**MATNTRNG** · August 9th 2010, 11:30 AM

Solve the equation algebraically for all values of x.

8x^3 + 4x^2 - 18x - 9 = 0

**Archie Meade** · August 9th 2010, 11:45 AM

Originally Posted by MATNTRNG

Solve the equation algebraically for all values of x.

8x^3 + 4x^2 - 18x - 9 = 0

Notice that this is

$(2x)^3+(2x)^2-9(2x)-9=0$

$2x=-1$ is a solution, so (2x+1) is a factor.

$(2x+1)\left(4x^2+bx-9)$ are the factors, so you only need find "b" and factor the quadratic.

**masters** · August 9th 2010, 11:47 AM

Originally Posted by MATNTRNG

Solve the equation algebraically for all values of x.

8x^3 + 4x^2 - 18x - 9 = 0

Hi MATNTRNG,

First, factor by grouping.

$8x^3+4x^2-18x-9=0$

$(8x^3+4x^2)-(18x+9)=0$

$4x^2(2x+1)-9(2x+1)=0$

$(4x^2-9)(2x+1)=0$

I'll bet you can take it from here. Right?

**Plato** · August 9th 2010, 11:48 AM

Originally Posted by MATNTRNG

Solve the equation algebraically for all values of x.

8x^3 + 4x^2 - 18x - 9 = 0

$8x^3+4x^2-18x-9=4x^2(2x+1)-9(2x+1)$

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