Every straight line can be written in the form y=mx+c.(If they seem completely unfamiliar with concept):M is known as the gradient of the line, which says how steep the line is. The bigger the number, the steeper the line.For example: A line with the equation y=x will look like this and y=4x like this. (label points on line to axis at x=1). As you can see, everytime we move 1 on the x axis, we move up 1 on the y axis for y=x, and up 4 on the y axis for y=4x. Another way this m, the gradient, can be written is dy/dx. This means the difference in y divided by the difference in x, so how much our value of y changes for each unit we change x. For example, on our question, we can find the difference in y between these two points by minusing one y value from the other. We can then find the difference in x by minusing one x value from the other. (y2-y1/x2-x1). This gives us the gradient of the graph.
The C in the equation stands for the Y-intercept or the coefficient of the line. This means what number it crosses the y axis at. Or what value Y is when x=0. (show that when x=0, it crosses the y axis). If we have not been given this value, we can find it by using the coordinates we do have. By putting the values in at Y and X for one of the coordinates we do have and the gradient, we can rearrange to find C.

4x+2y=22, (y/2)+(x/4)=2.5

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