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Unit 6: Integration and Accumulation of Change
6.6 Integration by Substitution
Applying the substitution method:
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Cards (73)
The composite function f(g(x))</latex> must have
g
′
(
x
)
g'(x)
g
′
(
x
)
present in the integrand.
True
What is the substitution for the integral
∫
sin
(
5
x
)
d
x
\int \sin(5x) \, dx
∫
sin
(
5
x
)
d
x
?
u
=
u =
u
=
5
x
5x
5
x
When finding
d
u
du
d
u
, you differentiate
u
u
u
with respect to x
Match the aspect with its substituted expression:
Original Variable ↔️
x
x
x
Substituted Function ↔️
f
(
u
)
f(u)
f
(
u
)
Substituted Derivative ↔️
d
u
du
d
u
When applying the substitution method, the first crucial step is to identify the appropriate part of the
integrand
In the substituted integrand,
g
(
x
)
g(x)
g
(
x
)
is replaced by
u
u
u
True
In the example
∫
sin
(
5
x
)
d
x
\int \sin(5x) \, dx
∫
sin
(
5
x
)
d
x
, the function to substitute is
u
=
u =
u
=
5
x
5x
5
x
True
The derivative
d
u
du
d
u
is found by differentiating
u
u
u
with respect to
x
x
x
True
In the example
∫
x
e
x
2
d
x
\int x e^{x^{2}} \, dx
∫
x
e
x
2
d
x
, the choice of
u
u
u
is
x
2
x^{2}
x
2
True
When rewriting the integral, the differential
d
x
dx
d
x
is replaced by du
In the example
∫
sin
(
5
x
)
d
x
\int \sin(5x) \, dx
∫
sin
(
5
x
)
d
x
, the substituted integral is \frac{1}{5} \int \sin(u) \, du
What is the next step after identifying the appropriate part of the integrand to substitute and choosing the new variable
u
u
u
and its differential
d
u
du
d
u
?
Rewrite the original integral
In the substitution method, the original variable
x
x
x
is replaced with the new variable \blanku
After solving the new integral, the variable
u
u
u
must be replaced with its original expression in terms of \blankx
When applying the substitution method, it is necessary to find a function
u
u
u
and its derivative
d
u
du
d
u
within the integrand
True
The derivative
d
u
du
d
u
of
u
=
u =
u
=
g
(
x
)
g(x)
g
(
x
)
is given by du = g'(x) \, \blankdx
To choose a suitable
u
u
u
, look for a composite function in the integrand.
True
The term
g
′
(
x
)
d
x
g'(x) \, dx
g
′
(
x
)
d
x
must be present or derivable from the original integrand to apply the substitution method.
True
What replaces the derivative
g
′
(
x
)
d
x
g'(x) \, dx
g
′
(
x
)
d
x
in the substituted integral?
d
u
du
d
u
After solving the new integral in terms of
u
u
u
, substitute
u
u
u
back with g(x).
The constant of integration
+
+
+
C
C
C
is added because the derivative of a constant is zero.
True
What is the final expression of the integral after substituting back
u
u
u
with
g
(
x
)
g(x)
g
(
x
)
?
F
(
g
(
x
)
)
+
F(g(x)) +
F
(
g
(
x
))
+
C
C
C
What is the result of integrating
1
5
∫
sin
(
u
)
d
u
\frac{1}{5} \int \sin(u) \, du
5
1
∫
sin
(
u
)
d
u
?
−
1
5
cos
(
u
)
+
- \frac{1}{5} \cos(u) +
−
5
1
cos
(
u
)
+
C
C
C
Why is it important to substitute back the original variable
x
x
x
after solving the integral in terms of
u
u
u
?
Express in original variable
Adding
+
+
+
C
C
C
to an indefinite integral represents all possible antiderivatives
In the substitution method, we identify a function
u
u
u
and its derivative du
For the integral
∫
(
2
x
+
3
)
4
d
x
\int (2x + 3)^{4} \, dx
∫
(
2
x
+
3
)
4
d
x
, the derivative
d
u
du
d
u
is
2
d
x
2 \, dx
2
d
x
Match the aspect of the integrand with its substitution:
Function to Substitute ↔️
g
(
x
)
g(x)
g
(
x
)
Derivative to Use ↔️
g
′
(
x
)
d
x
g'(x) \, dx
g
′
(
x
)
d
x
Goal ↔️ Simplify the integral
The derivative du</latex> must be present or derivable from the original
integrand
.
True
The substitution method involves finding a function
u
u
u
and its derivative
d
u
du
d
u
within the integrand.
True
Why should choosing the right substitution simplify the integral?
To make evaluation easier
What is the derivative of
u
=
u =
u
=
2
x
+
2x +
2
x
+
3
3
3
?
d
u
=
du =
d
u
=
2
d
x
2 \, dx
2
d
x
Steps to choosing a suitable
u
u
u
for substitution
1️⃣ Look for composite functions
f
(
g
(
x
)
)
f(g(x))
f
(
g
(
x
))
2️⃣ Choose
u
=
u =
u
=
g
(
x
)
g(x)
g
(
x
)
3️⃣ Find the derivative
d
u
=
du =
d
u
=
g
′
(
x
)
d
x
g'(x) \, dx
g
′
(
x
)
d
x
4️⃣ Ensure
g
′
(
x
)
d
x
g'(x) \, dx
g
′
(
x
)
d
x
is derivable from the integrand
What is the derivative of
u
=
u =
u
=
3
x
+
3x +
3
x
+
5
5
5
?
du = 3 \, dx</latex>
The derivative du</latex> must always be present in or derivable from the original
integrand
True
In the example \int (2x + 3)^{4} \, dx</latex>, after substitution, the new integral is
1
2
∫
u
4
d
u
\frac{1}{2} \int u^{4} \, du
2
1
∫
u
4
d
u
True
If u = 5x</latex>, then <latex>du = 5 \, \blankdx
Match the step of the substitution method with its description:
Solving the New Integral ↔️ Integrate
f
(
u
)
d
u
f(u) \, du
f
(
u
)
d
u
to find the indefinite integral in terms of
u
u
u
Substituting Back ↔️ Replace
u
u
u
with its original expression
g
(
x
)
g(x)
g
(
x
)
Adding the Constant ↔️ Include
+
+
+
C
C
C
to represent the constant of integration
What is the final integral of
∫
sin
(
5
x
)
d
x
\int \sin(5x) \, dx
∫
sin
(
5
x
)
d
x
after substitution and evaluation?
−
1
5
cos
(
5
x
)
+
- \frac{1}{5} \cos(5x) +
−
5
1
cos
(
5
x
)
+
C
C
C
Match the aspect of the substitution method with its description:
Original Integrand ↔️
∫
f
(
g
(
x
)
)
d
x
\int f(g(x)) \, dx
∫
f
(
g
(
x
))
d
x
Substituted Integrand ↔️
∫
f
(
u
)
d
u
\int f(u) \, du
∫
f
(
u
)
d
u
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