## Friday, November 20, 2015

### [EM_20151120QGXS] Quadratic Graphs by Completing the Square

Question

Introduction
This “Elementary” Mathematics question is usually pitched at secondary 3 (» grade 9).  It is quite a standard type of question, but from my experience, many students do not know how to begin.  The wording of the question (especially part (a)) may throw off some people.  The first stage in solving any mathematics question is always to make sure you understand the question, to know what is expected of you.  Once this is done, this question is actually quite straightforward if you know what to do and know where to look.  The coefficient of  x2  is  a = 1, so the question is not that tricky.  Part (a) is simply instructing you to complete the square.

Review

Solution

Tip:  You could get the y-intercept by using your fingers to cover the x2 and x terms.  There is an even faster way: just look at the constant term!  You get the answer  5  immediately!

H02. Use a diagram / model
H04. Look for pattern(s)
H05. Work backwards
H09. Restate the problem in another way
H11. Solve part of the problem

Suitable Levels
GCE ‘O’ Level “Elementary” Mathematics
any syllabus that includes quadratic functions and parabolas
anyone who is interested