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Posted by on Sunday, April 14, 2013 at 7:57am.

Null factor law and factoriising:
2x^2+7x=0
X(2x+7)=0
X=0 or 2x+7=0. ( the answer in the book was x=-7/2, how?

And. X^2-4=2x-4
Is it x^2-4-2x+4=o ??? If so!' how do I continue?

  • Math - , Sunday, April 14, 2013 at 9:41am

    2x^2+7x=0
    X(2x+7)=0
    X=0 or 2x+7=0
    ok so far

    Now, if the product of two numbers (A)(B) = 0
    that can only be true of one of the, or both , are equal to zero.
    (try multiplying any two numbers to get a result of 0)

    so either x=0 or 2x+7 = 0
    x = 0 says it all
    in
    2x+7 = 0
    2x = -7 , (simple equation rule)
    x = -7/2 , (simple equation rule)

    your second question:

    x^2 - 2x = 0 , after you take everything to the left
    x(x-2) = 0
    same as above and even simpler.

  • Math - , Sunday, April 14, 2013 at 9:49am

    2 x ^ 2 + 7 x = 0

    x ( 2 x + 7 ) = 0

    Obviously solution x = 0

    2 x + 7 = 0 Subtract 7 to both sides

    2 x + 7 - 7 = 0 - 7

    2 x = - 7 Divide both sides by 2

    x = - 7 / 2


    Solutions x = 0 and x = - 7 / 2


    x ^ 2 - 4 = 2 x - 4 Add 4 to both sides

    x ^ 2 - 4 + 4 = 2 x - 4 + 4

    x ^ 2 = 2 x Subtract 2 x to both sides

    x ^ 2 - 2 x = 2 x - 2 x

    x ^ 2 - 2 x = 0

    x ( x - 2 ) = 0

    Obviously solution x = 0

    x - 2 = 0 Add 2 to both sides

    x - 2 + 2 = 0 + 2

    x = 2


    Solutions x = 0 and x = 2

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