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    slack's Avatar
    slack Posts: 9, Reputation: 1
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    #1

    Jan 28, 2009, 08:48 PM
    Solving Functions
    If f(x)=3x^2+8 and g(x)=4x+21, then what is (f times g)(-5)? The answer is 11, but I do not know how to work it out.
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
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    #2

    Jan 29, 2009, 10:27 AM
    That is not a 'times'. It is a composition. Find

    or maybe it's written as

    That little circle is not a times symbol. It means composition.

    That means sub one function in for x into the other.

    Like so:



    Now, plug in x=-5

    By saying 'times' it means which is entirely different and not what the problem means.
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