posted by Elisabeth

Is x^2 - 2x
1 to 1?

I keep getting yes every way I try to work it. Book says no. In the end, I get (with x1=1 and x2=-1 <- I use these numbers because of the x^2) f(x1) = -1 and f(x2)=3. I can't seem to find if x1 = x2

(btw, I know that by the graph it is not, but I am trying to work it out the books way)

  1. Elisabeth

    I should add that my prof said in the notes that if the two answers to the two functions are the same, then it is not 1 to 1 BECAUSE they have the same answer. That's what has me confused.

  2. MathMate

    One-to-one is usually associated with an interval. If the interval is not mentioned, we will assume that it is (-∞∞).

    To find out if a function
    f(x) is one-to-one on the interval, we need to know if it is possible to find different values of x1 and x2 for which f(x1)=f(x2), where x1-x2≠0.

    If f(x1)=f(x2) then f(x) is not one-to-one on the given interval.

    For example,
    f(x)=x² on the interval (-∞,∞),
    we can find
    f(-1)=f(1), or f(-2)=f(2), therefore f(x)=x² is NOT one-to-one.

    The horizontal line test says that if you can draw a horizontal line and intersect the function at two or more points, the function is NOT one-to-one. On the other hand, if it is impossible to do so, the function is one-to-one.

    Try out your problem and post if you have other questions.

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