Questions: Find the difference quotient of f; that is, find (f(x+h)-f(x))/h, h ≠ 0, for the following function. Be sure to simplify.
f(x) = 2x² + x + 3
Transcript text: Find the difference quotient of $f$; that is, find $\frac{f(x+h)-f(x)}{h}, h \neq 0$, for the following function. Be sure to simplify.
\[
f(x)=2 x^{2}+x+3
\]
Solution
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Find the difference quotient \(\frac{f(x+h)-f(x)}{h}\) for \(f(x) = 2x^2 + x + 3\).
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Calculate \(f(x+h)\)
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\(f(x+h) = 2(x+h)^2 + (x+h) + 3\). Expanding \((x+h)^2\) gives \(x^2 + 2xh + h^2\). Thus, \(f(x+h) = 2(x^2 + 2xh + h^2) + x + h + 3 = 2x^2 + 4xh + 2h^2 + x + h + 3\).
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Calculate \(f(x+h) - f(x)\)
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\(f(x+h) - f(x) = (2x^2 + 4xh + 2h^2 + x + h + 3) - (2x^2 + x + 3)\). Simplifying, the terms \(2x^2\), \(x\), and \(3\) cancel out, leaving \(4xh + 2h^2 + h\).
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Calculate \(\frac{f(x+h)-f(x)}{h}\)
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\(\frac{f(x+h)-f(x)}{h} = \frac{4xh + 2h^2 + h}{h}\). Factoring out \(h\) gives \(\frac{h(4x + 2h + 1)}{h}\). Since \(h \neq 0\), cancel \(h\) to get \(4x + 2h + 1\).
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The difference quotient is \(4x + 2h + 1\).
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The difference quotient for $f(x)=2 x^{2}+x+3$ is $4x + 2h + 1$.