Sketching Quadratic Graphs by Completing the Square (part 1) : ExamSolutions

In this maths video tutorial I show you how we can use completing the square to sketch a quadratic graph, locate the maximum or minimum points and the equation of the line of symmetry. To see this and other tutorials go to http://www.examsolutions.co.uk/maths-tutorials/quadratic-functions/sketching_...

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• square
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[TheSilverSkylite]

My teacher taught us to square the number inside the bracket and then add it onto the other number. Like for example 1) (x - 4)sq would then go, in completed square form to (x - 4)sq + 16 + 6 and therefore (x - 4) sq + 22. Is that the wrong way to do them, because evidently your method would get a different answer to my teachers method :P

[ExamSolutions]

@TheSilverSkylite Yes it is the wrong way.

[runescapeo0o0]

by completing the square, can i find out the two x coordinates when y=0 like i would if i used the quadratic formula/factorised? i'm doing an exam on monday, its a mock of c1, all the AS maths students in my college are sitting the exam i'm just curious

[ExamSolutions]

@runescapeo0o0 Yes - check out my other videos on how to solve a quadratic equation by completing the square

[XxHelenaXAttwellxX]

These videos are just so helpful, my teacher always goes way to fast for me but I can just go home watch a few of these and I understand it :)

Thanks

[ExamSolutions]

@XxHelenaXAttwellxX Pleasure

[xEpicJ]

He sounds like alok jha from the guardian science weekly podcasts. Good work also!

[smokeeeeeeeee]

@Darkish04 It works with quadratics, y=(2x+1)^2 when multiplied out, y=4x^2+4x+1. Completing the square will work here. As for y=1/2x^2 that's simply a x^2 graph that has been stretched (squashed) parallel to the y-axis with a scale factor of 1/2. Completing the square is not needed here to sketch the graph

[Darkish04]

Does this only work with graphs with the common principle of ax^2 +bx+c , and not equations like y=(2x+1)^2 or y=1/2x^2? And if it does work with them; how would you come about solving them?

Thank you.

[runescapeo0o0]

@ExamSolutions yeah, i know how to solve it, but when i completed the square on a question today, i got 5 (sq. root) 2, but i had to sketch it which is where i was stuck. how would i sketch it then? because it's only a sketch, does the size of it matter? or should i just write on both sides the number which ill call A because i have forgotten it A +-5 (sq. root) 2? on either side? but on the negative size with the - and the positive side with the +