Basic graphs

. 

  

              1. Equation of a Straight Line                                 The equation of a straight line is usually written this way:

y = mx + c

What does it stand for?

		Slope intersept on y axis
y = how far up x = how far along m = Slope or Gradient (how steep the line is) C= the Y Intercept (where the line crosses the Y axis)

How do you find "m" and "c"?

• C is easy: just see where the line crosses the Y axis.
• m (the Slope) needs some calculation:

m  =

Change in Y Change in X

Knowing this we can work out the equation of a straight line:

Example 1

m

=

2 1

=

2

C = 1 (where the line crosses the Y-Axis)

So: y = 2x + 1

With that equation you can now ...

... choose any value for x and find the matching value for y

For example, when x is 1:

y = 2×1 + 1 = 3

Check for yourself that x=1 and y=3 is actually on the line.

Or we could choose another value for x, such as 7:

y = 2×7 + 1 = 15

And so when x=7 you will have y=15 

Example 2

m

=

3 -1

=

–3

C = 0

This gives us y = –3x + 0