How do you find the nonpermissable replacement for the variable in this expression?
3x/3x+2
:( I'm so confused.

Question

How do you find the nonpermissable replacement for the variable in this expression?
3x/3x+2
:( I'm so confused.

mertsj · Answer

That would be the values of x that cause the fraction to be undefined.  So we look for the values of x that make the denominator 0 and those are the nonpermissable replacements.

ragingsquirrel · Answer

Welcome to openstudy!

mertsj · Answer

$$3x+2=0$$
$$x=\frac{-2}{3}$$

mertsj · Answer

So that would cause the denominator to be 0 and so it is not permitted as a replacement.

anonymous · Answer

Thank you very much :)
I think I understand, but how do you figure out if they are equal to 0?

mertsj · Answer

You set it equal to 0 so you can find what value cannot replace x.

mertsj · Answer

Think of it this way.  It is illegal to have a denominator of 0.  So if the denominator is x, then it is illegal for x to be 0.
If the denominator is x-2 then it is illegal for x to be 2
If the denominator is x+3, then it is illegal for x to be -3
And so on...
And you can find these numbers by writing (denominator) = 0 and solving.  Then you will find the illegal numbers.