HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 74

A caveat when integrating symbolically…, it will not - cas calculator

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A caveat when integrating symbolically... This substitution process has one implication which you need to be wary of and so it is worth examining the process in more detail. The expanded version of what is happening is shown below. ∫S1 x2 0 − 1 dx = ⎡ x3 ⎢ ⎣ 3 ⎤ x=S1 − x⎥ ⎦ x=0 = ⎛ ⎜ S13 − ⎞⎛ S1⎟ − ⎜ 0 3 ⎞ −0⎟ ⎝ 3 ⎠ ⎝3 ⎠ = S13 − S1 3 The potential problem lies with the second line, where the substitution of zero results in the second bracket disappearing. This will not always happen. For example... ∫S1 ( x − 2)4 dx = ⎡ ⎢ ( x − 2)5 ⎤ ⎥ x= S1 0 ⎢⎣ 5 ⎦⎥ x=0 = ⎛ ⎜ ( S1 − 2)5 ⎞ ⎟ − ⎛ ⎜ (0 − 2)5 ⎞ ⎟ ⎜⎝ 5 5 ⎟⎠ (S1− 2)5 = −6⋅4 5 The final constant of 6.4 comes from substituting zero into the expression and should not be there if we were doing this with the aim of finding an indefinite integral. On the other hand, we all know that the answer should have a constant of integration, so perhaps this extra constant will help you to remember the '+c'! Calculator Tip There are strict limits to what the hp 39gs can integrate. For example, ∫ on the hp 39gs if you try to evaluate sin2 x.cos x dx it will not be able to do it. Essentially, little beyond polynomials. On the other hand, the hp 40gs is far more capable through its CAS (see page 324). The hp 40gs can handle integration by parts and by substitution as well as many other tricks. 74

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A caveat when integrating symbolically…
This substitution process has one implication which you need to be wary of and so it is worth examining the
process in more detail.
The expanded version of what is happening is shown below.
=
S
1
2
x
3
x
S
1
x
1
dx
=
x
0
3
x
=
0
3
3
S
1
0
=
S
1
0
3
3
S
1
3
=
S
1
3
The potential problem lies with the second line, where the substitution of zero results in the second bracket
disappearing.
This will not always happen.
For example…
=
S
1
4
(
x
2
)
5
x
S
1
(
x
2
)
dx
=⎢
0
5
x
=
0
5
(
S
1
2
)
(
0
2
)
5
=
5
5
5
(
S
1
2
)
64
=
5
The final constant of 6.4 comes from substituting zero into the expression and should not be there if we were
doing this with the aim of finding an indefinite integral. On the other hand, we all know that the answer
should have a constant of integration, so perhaps this extra constant will help you to remember the ‘+c’!
Calculator Tip
on the hp 39gs if you try to evaluate
2
x
x dx
able to do it.
There are strict limits to what the hp 39gs can integrate.
For example,
sin
.cos
it will not be
Essentially, little beyond polynomials.
On the other hand, the hp 40gs is far more capable through its CAS
(see page 324).
The hp 40gs can handle integration by parts and by
substitution as well as many other tricks.
74