Mathematics: Completing the square

Mathematics from high school to university
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Rating: 4.7 out of 5 (118 ratings)
5,134 students
1hr 53min of on-demand video
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Completing the square: how it is done and why the method works (variants for 1, 2, and 3 variables); a geometric illustration of the method and its name.
Completing the square in one variable for solving quadratic equations with help of the discriminant and the quadratic formula; derivation of the formula.
Completing the square in one variable for plotting polynomials of second degree with help of graph transformations of the parabola y=x^2; finding new vertex.
Completing the square in two variables, one at a time, for identifying conic sections: circles, ellipses, parabolas, and hyperbolas.
Completing the square in three variables, one at a time, for identifying quadric surfaces: spheres, ellipsoids, hyperboloids, double cones, etc.
Completing the square in two or three variables for definiteness of 2x2 or 3x3 matrices / corresponding quadratic forms in 2 or 3 variables.


  • Being able to perform operations of addition and multiplication of real numbers.


Mathematics: Completing the square

Mathematics from high school to university

1. Completing the square: how the method works, and why

You will learn about the method of completing the square, how it works and why. This remarkable (and elementary!) method has surprisingly many applications in advanced mathematics, and this is why it is really good to master it. Geometrical illustrations will give you a nice visual explanation of both the method and the name of the method.

2. A glimpse into some applications of completing the square

You will learn about various applications of completing the square, starting with quite elementary applications (high-school level) such as solving quadratic equations and drawing graphs of second degree polynomials, and continuing with some information about more advanced applications such as identifying quadratic curves and surfaces, determining definiteness of square matrices (or corresponding quadratic forms), and optimization of functions in two or more variables. These applications will not be treated in this course due to time constraints, but you will get information in which courses you find both theory and practice on the topics. You will also get some practice in completing the square. In this brief course I have chosen to inform you about applications of completing the square in Algebra, Calculus, and Linear Algebra and Geometry.

A note: Another typical application of completing the square (not discussed in this course) is in Calculus 2, when you must integrate a rational function (a function of the type p(x)/q(x), where both p(x) and q(x) are polynomials). After performing partial fraction decomposition, you will represent your function as a sum of simpler fractions, with denominators being first-degree polynomials or second-degree polynomials without real zeros. This second type, when integrated, will lead to some function defined by arctan; in order to perform this integration in a correct way (variable substitution), you must... complete the square! You can learn about partial fraction decomposition in my course "Precalculus 2: Polynomials and rational functions", and about the integration method mentioned above in my upcoming course "Calculus 2, part 1 of 2: Integrals with applications".

3. Extras

You will learn about our other (published) courses and about the courses we plan to create in the near future.

Who this course is for:

  • High school students who want to learn the method of completing the square and who are curious about its applications in university topics.
  • University or college students who have discovered that they need the method of completing the square for some university level courses, and they want to re-learn this method.
  • Everybody who wants to learn a remarkable but elementary method, which has surprisingly many applications in various advanced branches of mathematics.


University teacher in mathematics, PhD
Hania Uscka-Wehlou
  • 4.9 Instructor Rating
  • 2,057 Reviews
  • 18,741 Students
  • 13 Courses

I am a multilingual mathematician with a passion for mathematics education. I always try to find the simplest possible explanations for mathematical concepts and theories, with illustrations whenever possible, and with geometrical motivations.

I worked as a senior lecturer in mathematics at Uppsala University (from August 2017 to August 2019) and at Mälardalen University (from August 2019 to May 2021) in Sweden, but I terminated my permanent employment to be able to create courses for Udemy full-time.

I am originally from Poland where I studied theoretical mathematics and got pedagogical qualifications at the Copernicus University in Torun (1992-1997). Before that, I enjoyed a very rigorous mathematical education in a mathematical class in high school "Liceum IV" in Torun, which gave me a very solid foundation for everything else I have learned and taught later.

My PhD thesis (2009) was at Uppsala University in Sweden, with the title: "Digital Lines, Sturmian Words, and Continued Fractions".

In 2018 I received four pedagogical prizes from students at the Faculty of Science and Technology of Uppsala University: on May 13th from the students at the Master Program in Engineering Physics; on May 25th from the students at the Master Program in Electrical Engineering; on December 20th from the students at the Master Program in Chemical Engineering; on January 10th 2019 from UTN (Uppsala Union of Engineering and Science Students at Uppsala University).

I speak Polish, Swedish, English, Dutch, and some Russian; learning Ukrainian.

Editor at MITM AB
Martin Wehlou
  • 4.9 Instructor Rating
  • 2,057 Reviews
  • 18,741 Students
  • 13 Courses

I have a background in medicine and software development. I've done enough mathematics to at least follow along in Hania's courses and I'm learning a lot as I edit the material. I have also written a book about medical software design as it pertains to the medical record ("Rethinking the electronic healthcare record"). For Hania's math courses, it's my job to set up the environment and produce the final output that goes into these courses.

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