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Math Help - slope : tangent

  1. #1
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    slope : tangent

    If f(x)=5/(x^2+1) and g(x)=3x, then g(f(2))= ?

    i just need someone to reminde me about the substitution process.

    is it like... 5/[(3x)^2+1] or 3[5/(x^2+1)]
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    Quote Originally Posted by DINOCALC09 View Post
    If f(x)=5/(x^2+1) and g(x)=3x, then g(f(2))= ?

    i just need someone to reminde me about the substitution process.

    is it like... 5/[(3x)^2+1] or 3[5/(x^2+1)]
    the second one
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by DINOCALC09 View Post
    If f(x)=5/(x^2+1) and g(x)=3x, then g(f(2))= ?

    i just need someone to reminde me about the substitution process.

    is it like... 5/[(3x)^2+1] or 3[5/(x^2+1)]
    g(f(x)) means you take the function f and plug it into g. just like how g(3) means you take the number 3 and plug it into g...same concept, only you're plugging in a function, not a number.

    so, g(f(x)) = 3(f(x)) = 3 \left( \frac 5{x^2 + 1} \right) = \frac {15}{x^2 + 1}

    however, with these computational questions, i think it's easier to evaluate f(2) and then plug that number into g. it's usually easier that way...to me
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