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# How do you draw a straight-line graph using y = mx + c ?

2 years ago

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2 Replies

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2492 views

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Shania Cruickshank

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Experienced Maths tutor, infectiously enthusiastic

c represents the y axis intercept (where the graph crosses the y axis)

Start by plotting the point (0,c) which your line passes through

Then plot a second point using the gradient..

e.g. if m = 2 then increasing x by 1 increases y by 2, so (1, c+2) will be your next point on the graph

Plot a line through these points

Remember that negative gradient means an increase of 1 for x causes a decrease of m for y

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D
Dawn M

First mark the point where the line will cross the y axis which is at y = c.

Then the gradient m tells you which way your line should slope and also how many to go up or down for every 1 unit across. If m is positive the lines slopes like this / and if it is negative it slopes like this \.

To plot the line, first plot a second point starting from the first point you marked at y = c. You do this by going across one unit horizontally and if m is + then you go up by m units and if m is - you go down by m units.

Once you have your second point it is worth repeating the process to get a third point for safety and then you can draw a line that goes through all 3 points.

Example: y = 2x + 3

First point will be (0, 3)

Next point will be (1, 3+2) = (1, 5)

Next point will be (2, 5 + 2) = (2, 7)

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