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Maths

Parallel and perpendicular lines - Higher

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y = mx + c

We have seen graphs in the form y = mx + c before.

When a graph is written in the form y = mx + c, m represents the gradient and c represents the y intercept.

Take the example of the cost of a taxi ride at £1 + £3 per mile. In this case the gradient is the cost per mile and the intercept the £1 standing charge.

This can be written as y = 3x + 1

This line has a gradient of 3 and a y intercept of 1.

We can use this information to plot the graph, without drawing a table.

The line cuts the y-axis at 1 so the y intercept is 1.

image: graph of y = 3x + 1

The line has a gradient of 3 because every time it goes along one square it moves up 3 squares (every mile costs £3).

Question

Plot the graph of y = -x + 2 without using a table

toggle answer

Answer

m = -1 and c = 2, so the line cuts the y axis at 2 and has a gradient of -1.

The graph should look like this:

image: graph of y = minus x + 2

Remember, if the gradient is negative, the graph will slope up to the left.

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