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Sketch the graph of a twice-differentiable function `y=f(x)` whose derivatives have the following sign patterns below. Also you are given:`f(1)=f(4)=0, \text{ }f'(1)=f'(3)=0,\text{ }f''(2)=0`.
Interval | `(-oo,1)` | `(1,3)` | `(3,oo)` |
`f'(x)` | `\text{ }-` | `\text{ }+` | `\text{ }-` |
Interval | `(-oo,2)` | `(2,oo)` |
`f''(x)` | `\text{ }+` | `\text{ }-` |
To sketch this function, focus on the key features provided by the sign patterns of `f'(x`) and `f''(x)`, as well as the given points where `f(x) = 0`, `f'(x) = 0`, and `f''(x) = 0`. Start by plotting these critical points. Then, use the sign of `f'(x)` to determine where the function is increasing or decreasing, and the sign of `f''(x)` to determine the concavity. Remember that a change in the sign of `f'(x)` indicates a local extremum, while a change in the sign of `f''(x) ` indicates an inflection point.
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