 #### Revision Notes

##### What are coordinates?

When we want to plot a point on a graph we need to know where to put it.

If the horizontal axis is labelled x and the vertical axis is labelled y then the x and y coordinates are how far we go along the x and y axes respectively to plot the point.

##### What can we do with coordinates?

If we have two points with coordinates (x1, y1) and (x2, y2) then we should be able to find

• the gradient of the line through them
• the midpoint of the two points
• the distance between the two points

Don’t get fazed by the horrid notation (x1, y1) – this is just “point 1” and the other is “point 2” so we put the little numbers (subscripts) in so that we know which coordinate we are referring to. In questions there’ll be lots of nice numbers.

Here’s how we do each of those:

image You should also know that three points A, B and C lie on the same STRAIGHT LINE if AB and AC (or BC) have the same gradient

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