### Summary of Maths Lesson(19 August 2010)

What have we done in today Maths lesson?

1. We had revised that gradient is equal to rise over run. Gradient is also the difference in y value over the difference in x value.

2. The order of the coordinates is also important. We can write in the form of y2-y1/x2-x1, but not y2-y1/x1-x2, as the order is all wrong.

3. The points that coincide with the vertical line, or the y axis, has a gradient of zero(or infinite values) as they all have the same x coordinates. On the other hand, the points that coincide with the horizontal line, or the x axis, has a gradient of zero(or infinite values) as they all have the same y coordinates.

4. We also tried to do questions which asked us to find the value of c, or the constant. We first had to find m, the gradient, before substituting the coordinates into the equation to find the x and y value.

5. We also concluded that all parallel lines have the same gradient. The lines that are vertical or horizontal have a gradient of zero.

Here is a question related to what we have been discussing today.

AB is a line. If A is (-2, 2) and B is (5, 4), what is the gradient of AB?
What is the equation of AB then?

1. Gradient : (4-2) / (5-(-2)) = 2 / 7

Equation : y = 2/7x + 18/7

2. Here's another question:

Let AB be a straight line.
If A is (0, 5) and B is (0, -5), what is the equation of line AB?

3. y = mx + c

Substitute (0, 5) in the equation:

5 = m(0) + c
5 = 0x + c
c = 5

y = 0x + 5
y = 5