Completing the Square by Factoring Out -1

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Taught by mrbrianmclogan
  • Currently 3.0/5 Stars.
4671 views | 1 rating
Part of video series
Meets NCTM Standards:
Errors in this video:

At about the 0:34 mark, the teacher says our goal is to get it into...standard form; he should have said get it into vertex form.

At about the 4:42 mark, the teacher writes ±sqrt(5)=x+2; he should have written ±sqrt(5)=x-2. Because of this, he also gets the wrong zeros; he should get x=2±sqrt(5).

Lesson Summary:

This lesson teaches completing the square by factoring out -1. After isolating the x-terms and making it into a binomial square, students can add and subtract the constant value inside the trinomial, which can be multiplied by the -1 factor. This will provide a perfect square trinomial that can be written in binomial square format. Through solving for the zeros, students can determine the value of x, and avoid common mistakes such as not factoring out the negative one or forgetting to divide it first before taking the square root.

Lesson Description:

Completing the square by factoring out a negative one

I show how to solve math problems online during live instruction in class. This is my way of providing free tutoring for the students in my class and for students anywhere in the world. Every video is a short clip that shows exactly how to solve math problems step by step. The problems are done in real time and in front of a regular classroom. These videos are intended to help you learn how to solve math problems, review how to solve a math problems, study for a test, or finish your homework. I post all of my videos on YouTube, but if you are looking for other ways to interact with me and my videos you can follow me on the following pages through My Blog, Twitter, or Facebook.

Questions answered by this video:
  • How do I complete the square when there is a negative sign in front of the x^2 term?
  • How do I get a quadratic equation that is in standard form into vertex form?
  • How do I find the zeros of a quadratic function?
  • How do I complete the square on the function f(x)=-x^2+4x+1?
  • How do I get -x^2+4x+1 into vertex form?
  • What are the zeros of the function f(x)=-x^2+4x+1?
  • Staff Review

    • Currently 3.0/5 Stars.
    This lesson teaches how to complete the square on a quadratic function which gets the equation into vertex form. Then he shows how to find the zeros of the function once you have it in vertex form.