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Thread: Why is the answer a negative number?

  1. #1
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    Why is the answer a negative number?

    (-5a^3b^5)^2 / a^4b^3

    My working out and answer:

    (-5a^3b^5)(-5a^3b^5) / a^4b^3

    25a^6b^10 / a^4 b^3

    = 25a^2b^7

    The book says the answer= -25a^2b^7

  2. #2
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    Re: Why is the answer a negative number?

    Quote Originally Posted by einstein
    (-5a^3b^5)^2 / a^4b^3

    My working out and answer:

    (-5a^3b^5)(-5a^3b^5) / a^4b^3

    25a^6b^10 / a^4 b^3

    = 25a^2b^7

    The book says the answer= -25a^2b^7
    Following PEMDAS - both you and book are incorrect (according to the problem as posted).
    “... mathematics is only the art of saying the same thing in different words” - B. Russell

  3. #3
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    Re: Why is the answer a negative number?

    Quote Originally Posted by einstein
    (-5a^3b^5)^2 / a^4b^3
    Book is correct IF this is the expression: -(5a^3b^5)^2 / (a^4b^3)
    In other words: the - sign outside the brackets, PLUS denominator MUST be bracketed
    I'm just an imagination of your figment !

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    Re: Why is the answer a negative number?

    Quote Originally Posted by Subhotosh Khan
    Quote Originally Posted by einstein
    (-5a^3b^5)^2 / a^4b^3

    My working out and answer:

    (-5a^3b^5)(-5a^3b^5) / a^4b^3

    25a^6b^10 / a^4 b^3

    = 25a^2b^7

    The book says the answer= -25a^2b^7
    Following PEMDAS - both you and book are incorrect (according to the problem as posted).
    Can you please elaborate?

  5. #5
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    Re: Why is the answer a negative number?

    Quote Originally Posted by einstein
    [Can you please elaborate?
    Did you read Deniss's reply above??

    If you did - read it again slowly and carefully ......
    “... mathematics is only the art of saying the same thing in different words” - B. Russell

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    Re: Why is the answer a negative number?

    Quote Originally Posted by Subhotosh Khan
    Quote Originally Posted by einstein
    [Can you please elaborate?
    Did you read Deniss's reply above??

    If you did - read it again slowly and carefully ......
    yes i read his reply diligently

    he said the book is correct if there is a negative sign before the bracket and brackets around the last two terms... but there is not. i copied the the question from the book to the forum correctly and always do

    so denis is saying IF the book did it this way then the books answer is right. But the book did not do it the way he wrote, so that means the books answer is wrong. i got that!

    but you said BOTH the book's anwer was wrong (which, like i said, i get it) but you also said my answer was wrong. So i said please elaborate because i don't see how my answer is wrong. I believe i followed pemdas correctly. If you would kindly point out why MY answer was wrong i'd much appreciate it.

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    Re: Why is the answer a negative number?

    Your work:
    25a^6b^10 / a^4 b^3
    = 25a^2b^7

    That is incorrect (sorry, man!)
    As is (no brackets) 25a^6b^10 / a^4 b^3 means (25a^6b^10 / a^4) times b^3
    You PEMDASed badly
    I'm just an imagination of your figment !

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    Re: Why is the answer a negative number?

    Quote Originally Posted by Denis
    Your work:
    25a^6b^10 / a^4 b^3
    = 25a^2b^7

    That is incorrect (sorry, man!)
    As is (no brackets) 25a^6b^10 / a^4 b^3 means (25a^6b^10 / a^4) times b^3
    You PEMDASed badly
    thanks.

    so the answer to 25a^6b^10 / a^4 b^3 = 25a^2b^13

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    Re: Why is the answer a negative number?

    YESssssssssss
    I'm just an imagination of your figment !

  10. #10
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    Quote Originally Posted by einstein

    i copied the the question from the book to the forum correctly and always do
    If your book displays the given expression as shown below, then you did not correctly copy the exercise.

    [tex]\frac{(-5 a^3 b^5)^2}{a^4 b^3}[/tex]

    If your book displays the given expression the following way, instead, then you could clarify your typing with square brackets as shown in blue.

    [tex]\frac{(-5 a^3 b^5)^2}{a^4} \; b^3[/tex]

    [(-5a^3b^5)^2/a^4] b^3

    Either way, the factor of -1 is squared, so there is no negation sign in the answer.

    "English is the most ambiguous language in the world." ~ Yours Truly, 1969

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