Monday, 11 March 2013

Quadratic - Practice 9 (Denzel)

Practice 9

Find the value of k such that the equation x^2+kx+2k-3=0 has only one real root.



The question states that there is only one real root which would mean the discriminant would be zero as the roots are real and equal.

Now we work out the discriminant

a=1
b=k
c=2k-3

D=b^2-4ac
D=(k)^2-4(1)(2k-3)
k^2-8k+12=0

Now we use the general formula to find k as it is a quadratic equation
a=1
b=-8
c=12

Resulting in a final answer of

k=6 or 12

10 comments:

  1. very good, full mark answer 0_0.


    1.the concept about the relationship between discriminent and different types of roots is very clear.
    2.the process is very clear,easy for a marker to understand.
    3.the organization of the answer is neat ,clear and complete.


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  2. There are no conceptual errors. Explanation is easy to understand. Organization of answers is easy to follow and train of thoughts is easily understood.

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  3. Step are in order and very well shown. Reader can easily understand and follow along. The mathematical concepts are also very clear :D

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  4. 1) Able to understand the question and know that D=0 due to only 1 real root. Able to explain each step correctly

    2) Could have shown more of the steps such as the general formula . Other than that , the working is quite smooth .

    3) Neat and well organized .

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  5. The mathematical concept is clear with no conceptual errors
    He explained the question well allowing the reader to follow what he was doing
    The organisation is good and he clearly stated all the steps he used to get his answer

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  6. Concept is very clear.
    Organisation of steps was extremely good. Steps and working was easy to understand
    Explanation was also good since he explained the purpose of every step

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  7. Concepts are clear and explained before each step.
    Organization is good allowing the reader to follow the steps well.

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  8. Your explanation is very detailed and comprehendible, and shows that you understand all the topics used to answer. Also, your working is very neat and legible. :)

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  9. The discriminant should be just real and equal, not necessarily equal to 0. k=12 should be rejected as when it is subbed in to the equation there is more than 1 value of x. And the condition is that there is only 1 value of x.

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  10. Mr Johari said the answer is k = 6 or 2 ._.

    ReplyDelete