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stottrupbailey

  • 3 years ago

what's the inverse function of y= sqrt(x^2 + 7x) please help! :)

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  1. stottrupbailey
    • 3 years ago
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    \[y=\sqrt(x^2+7x)\]

  2. Prebz
    • 3 years ago
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    x(y) = 1/2 (-7±sqrt(4 y^2+49))

  3. stottrupbailey
    • 3 years ago
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    so far I have it down to \[x^2=y^2+7y \]

  4. stottrupbailey
    • 3 years ago
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    I'm just kind of confused

  5. zepdrix
    • 3 years ago
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    \[\large y=\sqrt{x^2+7x} \qquad \rightarrow \qquad x=\sqrt{y^2+7y}\]Squaring both sides,\[\large x^2=y^2+7y\]Let's complete the square on y, half of 7, squared, is \(\dfrac{49}{4}\).\[\large x^2+\frac{49}{4}=y^2+7y+\frac{49}{4}\] \[\large x^2+\frac{49}{4}=\left(y+\frac{7}{2}\right)^2\] I think maybe do something like this to deal with the different degrees of y. Does that make sense?

  6. stottrupbailey
    • 3 years ago
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    umm kind of... I'm a little lost at the part where you do the 49/4. This is a homework question online and they want a y= something, equation

  7. zepdrix
    • 3 years ago
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    Yah there would be a couple more steps to get it there :) ~Taking the square root of both sides,\[\large \pm\sqrt{x^2+\frac{49}{4}}=y+\frac{7}{2}\]

  8. zepdrix
    • 3 years ago
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    Confused about the `completing the square` step though?

  9. stottrupbailey
    • 3 years ago
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    yeah a little

  10. Prebz
    • 3 years ago
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    \[y=(\frac{ 1 }{ 2 } (-7±\sqrt{(4 x^2+49)})\]

  11. zepdrix
    • 3 years ago
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    \[\large x^2+bx\]To complete the square, we take half of the b term, and square it. That is the term we will want to ADD to complete the square.\[\large \left(\frac{b}{2}\right)^2 \qquad \rightarrow \qquad \frac{b^2}{4}\]So to complete the square we would add this term,\[\large x^2+bx+\frac{b^2}{4}\]And since it's a perfect square, we can write it as,\[\large \left(x+\frac{b}{2}\right)^2\]

  12. zepdrix
    • 3 years ago
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    Hmm completing hte square can be a little tricky if you don't remmeber how to do it :( I can't think of the best way to explain it.

  13. stottrupbailey
    • 3 years ago
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    the answer prebz gives is the right one, is that what you got zepdrix?

  14. zepdrix
    • 3 years ago
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    Yah that's the same :) His just has the 1/2 factored out, so it looks nicer.

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