Tuesday, 1 July 2014

Linear Graph: What's Wrong?

We were discussing the following question this morning (HW8E, Q1(d))

and I drew the diagram on the following on the board.

What I did: I 'identified two points (2,0) and (1, 0) to calculate the gradient of the line.

Then we were 'stuck' for quite some time.

Can you tell what's wrong with the working or the approach that I used?

What you need to do...
You are required to elaborate what has gone wrong when I approach this question.
Then suggest the points you should use to compute the gradient of the line; and tell us what is the final equation of the line.

[Attempt this by tonight 1 July, 2359]
[The first most complete response will be earn 5 points for your group]


  1. Both sets of coordinates are wrong.

    We need to remember that the first number is the x-intercept and the second number as y-intercept.

    The first ordered pair (0,-1) is wrong because at that point, the line did not cut the y-axis at -1, but at 0, the origin. The line cuts the y-axis at 0 , thus the coordinates should be (0,0).

    The second ordered pair (2,0) is wrong because at that point, the line did not cut y-axis at 0, but at -1. When you draw dotted lines extending from the x- and y- axis to the point, you will see that the coordinates are (2,-1).

    Therefore, to find out the gradient, you must take Rise/ Run.
    which is 0-(-1) / (0-2) = 1/ -2
    = -1/2( the answer)