Examples of Curve Sketching
Key Questions
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Information from
f(x)f(x) f(0)=1/{1+1}=1/2 Rightarrowf(0)=11+1=12⇒ y-intercept:1/212 f(x) > 0 Rightarrowf(x)>0⇒ x-intercept: nonelim_{x to infty}e^x/{1+e^x}=1 Rightarrow H.A.:y=1 lim_{x to -infty}e^x/{1+e^x}=0 Rightarrow H.A.:x=0 So far we have the y-intercept (in blue) and H.A.'s (in green):
Information from
f'(x) f'(x)={e^xcdot(1+e^x)-e^xcdot e^x}/{(1+e^x)^2}=e^x/(1+e^x)^2>0 Rightarrow f is always increasing.Information from
f''(x) f''(x)={e^x cdot (1+e^x)^2-e^xcdot2(1+e^x)e^x}/{(1+e^x)^4} ={e^x(1+e^x)(1-e^x)}/{(1+e^x)^4}={e^x(1-e^x)}/{(1+e^x)^3} f''(x)>0 on(-infty,0) andf''(x)<0 on(0, infty) f is concave upward on(-infty,0) and downward on(0, infty) .Hence, we have the graph of
f (in blue):
Questions
Graphing with the Second Derivative
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Relationship between First and Second Derivatives of a Function
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Analyzing Concavity of a Function
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Notation for the Second Derivative
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Determining Points of Inflection for a Function
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First Derivative Test vs Second Derivative Test for Local Extrema
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The special case of x⁴
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Critical Points of Inflection
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Application of the Second Derivative (Acceleration)
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Examples of Curve Sketching