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Math Help - Wrong range, please help me fix it.

  1. #1
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    Wrong range, please help me fix it.

    My range is apparently wrong, how come? What am I doing wrong?

    y = 25(-7x-4)^64

    Range = {all real numbers >= 20}

    The domain is all real numbers.

    Thanks
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  2. #2
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    What happens when we plug in x = -\frac{4}{7} ?
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  3. #3
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    We get 0. So, the range is 0?
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  4. #4
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    Quote Originally Posted by bobbyboy1111 View Post
    We get 0. So, the range is 0?
    Do you get an output value of zero for every input value of x? Then how could the range, being the set of all outputs, be just the singleton set {0}?

    You have a variable expression raised to an even power. What then should the graph look like? If you plug the listed x-value in, what y-value do you get out? Can you get any smaller y-values out, given the form of the graph?

    What then is the range?

    Look at the graph, if you're not sure....
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  5. #5
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    Quote Originally Posted by stapel View Post
    Do you get an output value of zero for every input value of x? Then how could the range, being the set of all outputs, be just the singleton set {0}?

    You have a variable expression raised to an even power. What then should the graph look like? If you plug the listed x-value in, what y-value do you get out? Can you get any smaller y-values out, given the form of the graph?

    What then is the range?

    Look at the graph, if you're not sure....
    I'm not quite sure, I'm absolutely terrible with graphs When I plug in the listed x-value, I get 0 as my y value. Can you please show me how to do it correctly? Thanks much
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  6. #6
    MHF Contributor Amer's Avatar
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    Quote Originally Posted by bobbyboy1111 View Post
    My range is apparently wrong, how come? What am I doing wrong?

    y = 25(-7x-4)^64

    Range = {all real numbers >= 20}

    The domain is all real numbers.

    Thanks
    you can think like this

    y=25(-7x-4)^{64}

    y value can't be negative since the power is even so we now remove (-infinity , 0) as a range find x values that make it zero in your question y can be zero as you see from the other posts and if x become bigger y become bigger to so if x goes to infinity y goes to infinity
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  7. #7
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    Quote Originally Posted by bobbyboy1111 View Post
    I'm not quite sure, I'm absolutely terrible with graphs When I plug in the listed x-value, I get 0 as my y value. Can you please show me how to do it correctly? Thanks much
    Then you need to get better with graphs. To start with, I suggest you substitute values from the domain - as many as necessary - into the given function and plot points.
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