26: The domain is D( f ) = (−∞,0) ∪ (0,∞).
The function needs to be written as a split function, then find the second derivative.

Dividing points: The equation f ′′(x) = 0 has solution x = 3.
The second derivative does not exist at x = 1.

Intervals of concavity will be (−∞,0), (0,1], [1,3], and [3,∞). Determine concavity and points of inflection using a chart.

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