x - 3(2x +3x) = 8 - 5x

[drewmandan]

The first factor is usually just found by trial and error. I mean, you could do bisection or Newton's method or something, but it's always fair to assume that these questions have whole number factors because they don't want the student getting caught up in stupid details. By the way, how is it you don't know how to do this? Are you ahead of the class or something?

[Sandform]

Help me out here.

x - 3(2x + 3) = 8 - 5x

This is really a simple problem, I remember doing things like this one all the time but I forgot what I was supposed to do.

x - 6x - 9 = 8 - 5x
-5x - 9 = -5x + 8
-17 = 0

So then it becomes the same equation except with a different y intercept...


I don't know what went wrong. I remember getting problems with an answer like this but I forget how to do it. My first instinct is just to say x is undefined, or no solution but... I dunno.

So no solution or undefined?

[ninja9578]

Uh, your solving it incorrectly :P Pull all of x on one side, and all numbers on the other. You end up getting the same result, but it's easier.

0x = 17

x is undefined.

[Sandform]

Ty.

[drewmandan]

This is a really poorly stated question if that's how it was given. This should actually have been given as the intersection of the lines y = -5x -9 and y = -5x - 8. Looking at it that way, it's obvious, without doing the math, that there is no solution, because the lines are parallel.

[ninja9578]

Oh, it was a line intersect problem :P I hate y=mx+b format, I prefer parametric equations.

[Sandform]

This is a really poorly stated question if that's how it was given. This should actually have been given as the intersection of the lines y = -5x -9 and y = -5x - 8. Looking at it that way, it's obvious, without doing the math, that there is no solution, because the lines are parallel.


agreed that is why I put it as -5x -9 = -5x - 8 when I was writing it but I felt like I was missing something.

So is undefined and no solution the same thing btw? I feel like a moron but I haven't taken math in a few months.

[Oneironaut]

Let the record show...that I fucking hate math.

That is all.

Carry on.

[capoopy]

Let the record show...that I fucking hate math.

That is all.

Carry on.
Me too... but im good at it

[Neruo]

I forgot all about those funky techniques I learned in high school.

But doing it the hard way (by head, like counting (yea counting didn't completely die out in the 1950s, unfortunately),

And

0 seems to be the answer to x.

[drewmandan]

agreed that is why I put it as -5x -9 = -5x - 8 when I was writing it but I felt like I was missing something.

So is undefined and no solution the same thing btw? I feel like a moron but I haven't taken math in a few months.

No, they're not as far as I know. Undefined is when you divide by zero, and no solution is when a system is inconsistent (linear algebra term).


0 seems to be the answer to x.

Wrong. There is no solution.

[Serkat]

Me too... but im good at itYeah, I hate that. Im actually very good at math but the only thing I like about it is set theory and logic and some of analysis and calculus, perhaps gemoetry. Probability theory and statistics and all that jazz I totally hate.

[Sandform]

I ehat hmat.

x^3-3x^2-x+3=0

[drewmandan]

I ehat hmat.

x^3-3x^2-x+3=0

Factor theorem.

x=-1 is a factor. Now do some long division to get

(x+1)(x^2 -4x +3) = 0
(x+1)(x-3)(x-1)=0

solutions are x=-1, 1, 3

[Sandform]

Why is x=-1 a factor?

Well that is to say...is x=-1 something you just look for in a situation like this or is there some method to deciding that it is x=-1