Solved integral exercises, from basic to exam level
Twenty-one exercises with solutions: basic integrals, parts, substitution, partial fractions, cyclic and trigonometric integrals, areas, volumes of revolution, integral functions, improper integrals, rms value and area under a parabola, with graphs.
Exercises on indefinite, definite and improper integrals of the kind set in Calculus 1 (Mathematical Analysis 1) courses, in three levels: basic, with basic integrals, composite forms, integration by parts and elementary partial fractions; intermediate, with cyclic integrals, rational functions with irreducible denominators or repeated roots, trigonometric substitutions; exam, with areas, volumes, integral functions, improper integrals and an application to electrical engineering. The result is given straight away; the full solution opens with a click. The proofs and tables are in the in-depth study linked at the top.
Basic level
Exercise 1. Basic integrals
Compute
.
Result:
.
Solution
The integral is linear: integrate term by term.
;
;
.
The absolute value in the logarithm is needed because
is also defined for
, and there the antiderivative is
. Check: differentiating the result gives back the integrand.
Exercise 2. A composite form
Compute
.
Result:
.
Solution
The derivative of the exponent
is
, which appears (up to the factor 2) in front of the exponential. With
,
:
![]()
It is the form
. Beware:
, without the
in front, cannot be expressed with elementary functions.
Exercise 3. By parts
Compute
.
Result:
.
Solution
Differentiate the polynomial and integrate the cosine:
,
, so
,
.
![]()
The opposite choice (
,
) would lead to
, which is more complicated: the rule is to differentiate the factor that simplifies.
Exercise 4. Partial fractions
Compute
.
Result:
.
Solution
The denominator has
:
. Look for
, i.e.
.
With
:
,
. With
:
,
.
![]()
Exercise 5. Definite integral and area
Compute
and
. What is the area of the region between the graph of
and the
axis for
?
Result: 2; 0; the area is 4.
Solution
Fundamental theorem:
.
On
:
. The integral is zero because it counts with sign: the part below the axis, between
and
, is
and cancels the part above.
The area, which is always positive, is the integral of the absolute value:
. In area problems always study the sign of the function first.

Intermediate level
Exercise 6. The logarithm
Compute
.
Result:
.
Solution
By parts with the factor-1 trick:
,
, so
,
.
![]()
The same trick works for
,
and
.
Exercise 7. A cyclic integral
Compute
.
Result:
.
Solution
Let
be the integral. By parts with
,
:
.
Again by parts with
,
:
.
Substituting:
, so
and
.
Important: in both integrations by parts you must differentiate the same family of functions (here the trigonometric ones); switching at the second step brings you back to the original integral with a useless identity.
Exercise 8. Irreducible denominator
Compute
.
Result:
.
Solution
: the denominator does not factor. Make its derivative,
, appear:
.
![]()
The first is
(no absolute value: the argument is always positive). For the second complete the square:
, and the formula of the in-depth study (
) gives
.
Exercise 9. A double root
Compute
.
Result:
.
Solution
With the double root
two fractions are needed:
, i.e.
.
With
:
. With
:
,
. Coefficient of
:
, so
.
![]()
Typical mistake: writing only
, forgetting the term
: the system would have no solution.
Exercise 10. The square of sine
Compute
.
Result:
.
Solution
Half-angle formula:
. So
![]()
By parts one gets the same result as a cyclic integral. Over a whole period the mean of
is
: this is the fact behind the rms value (exercise 20).
Exercise 11. The universal substitution
Compute
.
Result:
(for
).
Solution
No shortcut: use
, with
and
.
![]()
![Rendered by QuickLaTeX.com \[ \int\frac{dx}{2 + \cos x} = \int\frac{1 + t^2}{3 + t^2}\cdot\frac{2\,dt}{1 + t^2} = \int\frac{2\,dt}{t^2 + 3} = \frac{2}{\sqrt 3}\arctan\frac{t}{\sqrt 3} + C \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-5464aebe85fe2de150885b278ddaa946_l3.png)
On the whole line the antiderivative must be “joined up” at each odd multiple of
, where
is undefined; for definite integrals over
it is better to use symmetry:
.
Exercise 12. The square root of 1 minus x squared
Compute
and deduce the area of the circle of radius 1.
Result:
; area
.
Solution
With
,
, we have
(positive in that interval) and
:
![]()
Back to
:
,
.
The circle of radius 1 is four times the area between 0 and 1:
.

Exam level
Exercise 13. Area between two curves
Compute the area of the region bounded by the parabolas
and
.
Result:
.
Solution
Intersections.
, i.e.
. Between
and 1 the parabola
is on top (at 0 it is 2, against 0).
Area. Integrate “top minus bottom”:
![Rendered by QuickLaTeX.com \[ A = \int_{-1}^{1}\left[(2 - x^2) - x^2\right]dx = \int_{-1}^{1}(2 - 2x^2)\,dx = 2\int_0^1(2 - 2x^2)\,dx = 2\left(2 - \frac{2}{3}\right) = \frac{8}{3} \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-fcf18ba16daa0f108a85ae14a4537418_l3.png)
Symmetry was used: the integrand is even.

Exercise 14. Volumes of revolution
Compute the volume of the solid obtained by rotating about the
axis the graph of
for
, and the one obtained by rotating an arch of
for
.
Result:
;
.
Solution
Cut the solid into discs perpendicular to the axis, of radius
and thickness
: each has volume
. So
![Rendered by QuickLaTeX.com \[ V = \pi\int_a^b f(x)^2\,dx \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-f78a820bc2573c7c3077d53a7ed6aa65_l3.png)
For
:
. It is a paraboloid, and the result is half the circumscribed cylinder (
), as Archimedes found.
For sine:
, using exercise 10.

Exercise 15. By parts with arctangent
Compute
.
Result:
.
Solution
By parts differentiating the arctangent:
,
,
.
![Rendered by QuickLaTeX.com \[ \int_0^1 x\arctan x\,dx = \left[\frac{x^2}{2}\arctan x\right]_0^1 - \frac{1}{2}\int_0^1\frac{x^2}{1 + x^2}dx \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-a7037fa6a375074687dc392537b9c786_l3.png)
The first term is
. In the second divide:
, with integral
.
Result:
.
Exercise 16. Substitution then parts
Compute
.
Result:
.
Solution
With
, i.e.
,
:
.
By parts (
,
):
. Back to
:
.
Check by differentiating:
.
Exercise 17. Wallis integrals
Compute
in two ways.
Result:
.
Solution
With the recurrence formula (in-depth study):
.
With trigonometric formulas:
. Between 0 and
the integrals of
and
vanish, and what remains is
.
Exercise 18. Studying an integral function
Study
, given that
. Then compute the derivative of
.
Result:
is odd, increasing, with an inflection point at 0 and asymptotes
;
.
Solution
Derivative. By the fundamental theorem
:
is increasing on all of
. We study a function whose expression is unknown, only through its derivative.
Symmetry. The integrand is even, so
(with
):
is odd,
.
Concavity.
: convex for
, concave for
, inflection point at 0 with slope
.
Limits. As
,
(given in the problem); by symmetry
at
. Two horizontal asymptotes.
The composite function.
, so
.
The function
is called the error function,
: it is the probability that a normal random variable lies within a certain distance of its mean.

Exercise 19. An improper integral
Compute
.
Result: 1.
Solution
By definition it is
. By parts with
,
,
:
![Rendered by QuickLaTeX.com \[ \int_1^b\frac{\ln x}{x^2}dx = \left[-\frac{\ln x}{x}\right]_1^b + \int_1^b\frac{dx}{x^2} = -\frac{\ln b}{b} + 1 - \frac{1}{b} \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-5929de0c27555583995db8ea0d882642_l3.png)
As
,
and
: the integral converges and equals 1.
Convergence could be predicted by comparison:
for
, so the integrand is less than
, whose integral converges.
Exercise 20. The rms value
A current
flows in a resistor
. Compute the average power dissipated over one period, the rms value of the current, and the mean value of
.
Result:
;
; mean value
.
Solution
Average power.
. The period is
, and the average is
![]()
because the mean of
over a period is
(exercise 10, with the change
).
rms value. It is the direct current that would dissipate the same power:
, so
. The 230 V of the mains is an rms value: the peak is
V.
Rectified mean value.
. Cheap meters measure this and multiply it by
: they give the right rms value only for sinusoidal signals.

Exercise 21. The area under a parabola in the first quadrant
The parabola
meets the vertical axis at
and the horizontal axis at
, with
and
. Compute the area of the region of the first quadrant between the parabola and the two axes in two cases: (A) the parabola is tangent to the horizontal axis at
; (B) the axis of symmetry of the parabola coincides with the vertical axis. Compare the results with the area of the rectangle with sides
and
.
Result: (A)
, area
; (B)
, area
.
Solution
Why two cases are needed. There are three coefficients to find (
,
,
), and passing through
and
gives only two conditions:
and
. Without a third condition the parabola is not determined, and neither is the area. The two most natural conditions are tangency to the horizontal axis, case A, and symmetry about the vertical axis, case B.
Case A: tangent at
. If the horizontal axis is tangent at
, then
is a double root and the vertex is
:
. From
we get
, so
![Rendered by QuickLaTeX.com \[ f(t) = \frac{\alpha}{\beta^2}(t - \beta)^2 = \alpha\left(1 - \frac{t}{\beta}\right)^2,\qquad a = \frac{\alpha}{\beta^2},\ b = -\frac{2\alpha}{\beta},\ c = \alpha \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-b90b49a80ad59bf08352a298a6d455e9_l3.png)
everywhere, so the area is the integral. With the substitution
,
, and the limits
,
:
![Rendered by QuickLaTeX.com \[ A = \int_0^\beta\alpha\left(1 - \frac{t}{\beta}\right)^2dt = \alpha\beta\int_0^1u^2\,du = \frac{\alpha\beta}{3} \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-78f033484dd34e9d9036f11bffe8eb41_l3.png)
Case B: symmetric about the vertical axis. Then
and the vertex is
:
, with
, i.e.
. So
, positive between 0 and
:
![Rendered by QuickLaTeX.com \[ A = \int_0^\beta\alpha\left(1 - \frac{t^2}{\beta^2}\right)dt = \alpha\left[t - \frac{t^3}{3\beta^2}\right]_0^\beta = \alpha\left(\beta - \frac{\beta}{3}\right) = \frac{2}{3}\alpha\beta \]](https://www.electronics-engineering.com/wp-content/ql-cache/quicklatex.com-360b64ec73abfba523ef59a9b96978c0_l3.png)
The comparison. The rectangle containing the region has area
. In case A the parabola fills one third of the rectangle, in case B two thirds: the two regions are complementary, because the parabola of case A, flipped (
,
), gives exactly that of case B. The two-thirds result, the area of a parabolic segment relative to the circumscribed rectangle, was already known to Archimedes, who proved it without integrals by the method of exhaustion.
Numerical check. With
and
: case A
, area 2; case B
, area 4; rectangle 6.






