Find all real values such that there is exactly one solution

mxrie

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Aug 12, 2018
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Hello! So I am taking supplementary Math classes as a prerequisite and I’m having trouble with answering different exercises (possibly because I do not have a solid foundation). Anyway, we were given this exercise problem:

“Find all real values of k such that the equation [x^2+kx+k=x-2] has exactly one solution.”

I have a gist on what to so but I don’t exactly know how to do it...
So far, what I have done is:
  • rewrite the equation as [x^2 + x(k-1) + (k+2) = 0] so that it would be in standard form.

My teacher gave the clue that in order for the equation to have one solution, the discriminant (b^2-4ac) in the quadratic formula must equate to 0. So far, I think ‘b’ would be (k-1), ‘a’ would be 1, and ‘c’ would be (k+2). I know the only thing I probably have to do is substitute this and solve but I honestly do not understand how I’m supposed to do that nor do I know how that would look like.

I’m hoping that somebody here could show me a step by step process on how to solve this problem as a reference for future problems similar to this one. Thank you for your time!
 
You are definitely on the right track...and so equating the discriminant to zero, we have:

\(\displaystyle (k-1)^2-4(1)(k+2)=0\)

You now have a quadratic in \(\displaystyle k\) to solve...what do you find?
 
You are definitely on the right track...and so equating the discriminant to zero, we have:

\(\displaystyle (k-1)^2-4(1)(k+2)=0\)

You now have a quadratic in \(\displaystyle k\) to solve...what do you find?

OH OKAY!! I think I understand it now, thank you very much for your help! Is what I did below correct?
3CDEC143-48FE-4491-AF09-800FB4B91810.jpg
 
… I do not have a solid foundation …
That's easy to fix; practice as much as you can. At some point, you'll realize new material has become easier to understand.


… My teacher gave the clue that in order for the equation to have one solution, the discriminant (b^2-4ac) in the quadratic formula must equate to 0.
Do you understand why this clue works? I still remember the day I first realized why, and that realization led to another: a shortcut to use (before the next course taught the shortcut). :cool:

Good job, by the way. And kudos to you, for following the main points in our forum guidelines!
 
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