Texas A&M University-Corpus Christi
Dept. of Computing and Mathematical Sciences
MATH 2414 §002
Calculus II
Fall 2003
Chapter 7 Study Questions
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7.1 Integration by Substitution (Part I)
- Knowing the chain rule for differentiation is helpful for
finding antiderivatives.
- An incorrect guess cannot help find the correct
antiderivative.
- When making a substitution in the integral of 3x^2 cos(x^3),
the "inside function" is the cosine.
- The method of substitution is a formalization of the
guess-and-check method.
- The method of substitution always works when there is an
inside function and outside function.
- A common pattern for an integral is to have a function in the
denominator and its derivative in the numerator.
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7.2 Integration by Substitution (Part II)
- After making a substitution, the original limits of
integration are still used.
- In Example 2, the substitution made is w = cos theta .
- Sometimes you must solve the substitution w = f(x) for x
before finding dx.
- The integral of sqrt(1-x^2) from -1 to 1 is evaluated using
the Fundamental Theorem of Calculus in this section.
- The area of the ellipse x^2/a +y^2/b = 1 is pi/ab.
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7.3 Integration by Parts
- The first guess of x*e^x as an antiderivative of x*e^x can be
corrected by multiplying by a constant.
- Integration by parts comes from the chain rule for
derivatives.
- Integration by parts always evaluates an integral
directly.
- It helps if u' is simpler than u and v is simpler than
v'.
- Integration by parts does not apply to definite
integrals.
- It may be necessary to apply integration by parts more than
once.
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7.4 Tables of Integrals
- Most functions have elementary antiderivatives.
- One section in the table of integrals is "Cubes in the
Denominator."
- "Reduction formulas" may be used repeatedly.
- The polynomial x^2+6x+14 is a perfect square.
- Partial fractions requires the decomposition of a quotient
intotwo or more fractions and comes from the solution of several
equations inseveral unknowns.
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7.5 Approximating Definite Integrals
- Riemann sums are only calculated using left sums and right
sums.
- The midpoint rule is the average of the left and right
sums.
- The trapezoid rule gives an over estimate if the integral is
concave up.
- The midpoint rule gives an overestimate if the integral is
concave up.
- The trapezoid in Figure 7.6 has top edge drawn as a secant
line.
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7.6 Approximation Errors and Simpson's Rule
- Using left or right sums, each extra digit of accuracy
requires 10 times as many subintervals.
- Using the trapezoid or midpoint rules, each extra digit of
accuracy requires 10 times as many subintervals.
- If it takes a calculator half a second to evaluate a midpoint
approximately accurate to 4 digits, then it will take 50 seconds
to increase that approximation to 6 digits.
- The error in the trapezoid rule is half that of the midpoint
rule.
- In Simpson's rule, each extra 4 digits of accuracy requires
about 10 times as much work.
- Errors using Simpson's rule are proportional to n^4.
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7.7 Improper Integrals
- Improper integrals have an infinite limit or an unbounded
integrand.
- Taking a hydrogen atom apart requires moving the electron to
an infinite distance from the proton.
- It is possible to have an improper integral with both limits
being (positive and negative) infinity.
- An integrand can only become infinite at a one of the limits
of integration.
- An integral that doesn't converge is said to polyverge.
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7.8 More on Improper Integrals
- You may determine that an improper integral converges without
knowing its value.
- To show convergence, f(x), the integrand, needs to be larger
than one whose integral converges.
- The integral of 1/x^p from 1 to infinity converges for p >1
and diverges for p < 1.
- The integral of (sin x + 3)/sqrt(x) from 1 to infinity
diverges since the integral of 2/sqrt(x) from 1 to infinity
diverges and (sin x + 3)/sqrt(x) > 2/sqrt(x).
- In comparing two integrands, one must be larger than the other
over the entire interval of integration to decide about
convergence.