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Unit 5: Analytical Applications of Differentiation
5.6 Determining Concavity and Points of Inflection
Using the second derivative to determine concavity:
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Cards (68)
What does concavity refer to in the context of a graph?
The shape of a curve
What is the shape of a curve when it is concave down?
An upside-down bowl
What is the first derivative of
f
(
x
)
=
f(x) =
f
(
x
)
=
x
3
−
3
x
2
+
x^{3} - 3x^{2} +
x
3
−
3
x
2
+
5
5
5
?
3
x
2
−
6
x
3x^{2} - 6x
3
x
2
−
6
x
What rules are used to find the first derivative of a function?
Differentiation rules
Critical points occur where the
second derivative
is equal to zero or undefined.
True
The second derivative can be undefined at points where the
concavity
may change.
True
Concavity refers to the shape of a curve on a graph.
True
Match the concavity with its shape:
Concave Up ↔️ U
Concave Down ↔️ ∩
Steps to find the second derivative of a function:
1️⃣ Find the first derivative
2️⃣ Find the second derivative by differentiating the first
3️⃣ Simplify the second derivative
Critical points of the second derivative may occur where the second derivative is
undefined
.
True
If
f
′
′
(
x
)
>
0
f''(x) > 0
f
′′
(
x
)
>
0
in an interval, the function is concave up.
True
Steps to determine concavity in intervals based on the second derivative
1️⃣ Identify intervals based on critical points
2️⃣ Choose test values within each interval
3️⃣ Evaluate
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
at each test point
4️⃣ Interpret the sign of
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
to determine concavity
Match the concavity with the sign of
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
:
Concave Up ↔️ +
Concave Down ↔️ -
If
f
′
′
(
x
)
>
0
f''(x) > 0
f
′′
(
x
)
>
0
, the function is concave up.
True
A curve that looks like an upside-down bowl is called
concave
down.
What is the first step to find the second derivative of a function?
Find the first derivative
To find the critical points of the second derivative, you set
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
equal to zero.
If f''(0) = - 6</latex>, the function is concave down at
x
=
x =
x
=
0
0
0
.
True
A positive sign of the second derivative indicates the function is concave
up
For
x
=
x =
x
=
0
0
0
,
f
′
′
(
0
)
=
f''(0) =
f
′′
(
0
)
=
−
6
- 6
−
6
, indicating the function is concave down
To determine concavity in different intervals, we look at the sign of the second
derivative
How are critical points
a
a
a
and
b
b
b
found for concavity analysis?
f
′
′
(
x
)
=
f''(x) =
f
′′
(
x
)
=
0
0
0
Steps to identify points of inflection
1️⃣ Find
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
2️⃣ Set
f
′
′
(
x
)
=
f''(x) =
f
′′
(
x
)
=
0
0
0
and solve for
x
x
x
3️⃣ Check where
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
is undefined
4️⃣ Verify that the sign of
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
changes across each critical point
A concave up curve has a shape that resembles the letter
U
Steps to find the second derivative of a function
1️⃣ Find the first derivative
2️⃣ Find the derivative of the first derivative
3️⃣ Simplify the expression
The function
f
(
x
)
=
f(x) =
f
(
x
)
=
x
2
x^{2}
x
2
is an example of a curve that is always concave up
What does setting the second derivative equal to zero help us find?
Potential inflection points
What are critical points of the second derivative called?
Points of concavity change
What do critical points and points of undefined second derivative help determine?
Concavity intervals
What happens to the derivative when a curve is concave down?
It is decreasing
What is an example of a function that is concave up?
f
(
x
)
=
f(x) =
f
(
x
)
=
x
2
x^{2}
x
2
The second derivative of
f
(
x
)
=
f(x) =
f
(
x
)
=
x
3
−
3
x
2
+
x^{3} - 3x^{2} +
x
3
−
3
x
2
+
5
5
5
is 6x - 6
If
f
′
′
(
x
)
=
f''(x) =
f
′′
(
x
)
=
6
x
−
6
6x - 6
6
x
−
6
, what is the sign of
f
′
′
(
0
)
f''(0)
f
′′
(
0
)
?
Negative
To determine the concavity of a function, we look at the sign of the
second
derivative.
If
f
′
′
(
x
)
<
0
f''(x) < 0
f
′′
(
x
)
<
0
, the function is concave down.
True
To determine the concavity of a function, we look at the sign of the
second
derivative.
Match the concavity with the sign of
f
′
′
(
x
)
f''(x)
f
′′
(
x
)
:
Concave Up ↔️ +
Concave Down ↔️ -
A curve that looks like a bowl opening upwards is called
concave
up.
The second derivative of
f
(
x
)
=
f(x) =
f
(
x
)
=
x
3
−
3
x
2
+
x^{3} - 3x^{2} +
x
3
−
3
x
2
+
5
5
5
is
f
′
′
(
x
)
=
f''(x) =
f
′′
(
x
)
=
6
x
−
6
6x - 6
6
x
−
6
.
True
What does the sign of the second derivative indicate in an interval?
The concavity
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