Find $f(a)$, $f(a + h)$, and the difference quotient, given $f(x)=7-8x+2x^2$

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There is a small algebra mistake, notice $2(a+h)^2=2a^2+\color{red}4ah+2h^2$. From here your last line turns into $\frac{-8h+4ah+2h^2}{h}$, which simplifies to $-8+4a+2h$.

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TheNewGuy
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TheNewGuy

Updated on June 23, 2020

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  • TheNewGuy
    TheNewGuy over 3 years

    Question is here:

    I need help with part c.

    I tried plugging everything in and simplifying to a point where my final answer was $(-8h+2ah+2h^2)/h$

    My work:

    $(7-8a-8h+2(a+h)^2-7+8a-2a^2)/h$ combine like terms

    $(-8h+2(a+h)^2 -2a)/h$ foil/expand

    $(-8h+2a^2+2ah+2h^2-2a)/h$ combine like terms

    $-8h+2ah+2h^2/h$

    • Mufasa
      Mufasa over 8 years
      HINT: $h$ is a common factor of the numerator and the denominator and can therefore be cancelled out
    • Darrell
      Darrell over 8 years
      What is $2(a+h)^2$?
    • TheNewGuy
      TheNewGuy over 8 years
      Thanks everyone. I didn't realize I foiled it wrong because I did it quickly in my head.