# What constitutes a rational expression? How would you explain this concept to someone unfamiliar with it?   Can you help me answer this? Thanks

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durbanville | High School Teacher | (Level 2) Educator Emeritus

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A rational expression involves a division where two numbers form a ratio; for example `3/4` is a rational expression. Remember that the denominator (in the above example, the `4` ) cannot be 0 as this would render the expression as undefined.

When the example includes `x` or any variable in the denominator ; for example `3/(x-1)`  , this indicates that `x!=1`  because that would render the denominator as `1-1 = 0` and our expression would be undefined for `x=1` so would NOT represent a rational expression.

`(x+2)/(x+3)` This would be a rational expression for values other than `x=-3`  `therefore x!=-3` Or you could say that the expression is undefined at x= -3. For all other values it is a rational expression.

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