Algebraic expr: plug x+1/x-1 in for x in x+1/x-1; then....

[Nekkamath]

Suppose we replace each x in the expression x+1/x-1 with the expression x+1/x-1. What is the value of the resulting expression when x=4/5? Express your answer as a common fraction.

I thought they might cancel one another out when it got flipped. But I only got -1 which is not a common fraction. So I know that is wrong.

 

[Loren]

Re: Algebraic expression

x+1/x-1 means \(\displaystyle x+\frac{1}{x}-1\). Is this what you mean? If not, please use parenthesis to clarify.

P.S. You might evaluate the last expression first by plugging in the value of x, then plug that into the original expression and evaluate that.

 

[Nekkamath]

[(x + 1)/(x - 1) + 1]/[(x + 1)/(x - 1) - 1], or
[(9/5)(-1/5) + 1]/[(9/5)(-1/5) - 1], or
(-8)/-10 = 4/5

This is what one person came up for me. But I don't understand the numbers.

 

[stapel]

I don't understand the numbers.

The exercise tells you to evaluate the expression at x = 4/5. You are supposed to plug (x + 1)/(x - 1) in for "x" in (x + 1)/(x - 1), and find the value when x = 4/5. If x = 4/5, what then is the value of (x + 1)/(x - 1)?

You are then supposed to plug (x + 1)/(x - 1) (or the numerical result) in for "x" in (x + 1)/(x - 1). If you plug the result of the above into (x + 1)/(x - 1), what value do you arrive at?

Eliz.