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Math Help - Easy Multiple Choice

  1. #1
    Member Mr Rayon's Avatar
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    Wink Easy Multiple Choice

    A solution of x^3 - 9x^2 + 15x + 25 = 0 is x = 5. How many other (distinct) solutions are there?


    A) 0 B)1 C)2 D)3 E)4
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  2. #2
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    mr fantastic's Avatar
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    Quote Originally Posted by Mr Rayon View Post
    A solution of x^3 - 9x^2 + 15x + 25 = 0 is x = 5. How many other (distinct) solutions are there?


    A) 0 B)1 C)2 D)3 E)4
    x = 5 is a zero means that (x - 5) is a factor. This helps you factorise the cubic:

    (x - 5)(x^2 - 4x - 5) = 0.

    So how many distinct real solutions does x^2 - 4x - 5 = 0 have?
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  3. #3
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    Quote Originally Posted by Mr Rayon View Post
    A solution of x^3 - 9x^2 + 15x + 25 = 0 is x = 5. How many other (distinct) solutions are there?

    A) 0 B)1 C)2 D)3 E)4
    What did you see when you plugged the graph into your calculator? What did you get when you divided out the given factor "x - 5" (or else plugged the given zero, x = 5, into the synthetic division) and then applied the Quadratic Formula to the remaining factor?
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