Straight Line Graphs 10th November 2015

When X= 0
Y is whatever the intercept of the line is.

The gradience tells us how much to go up in each time

Sometimes you are given a graph of a straight line and you need to find its gradient.
To find the gradient of a straight line:

• choose any two points on the line
• draw a right-angled triangle with the line as hypotenuse
• use the scale on each axis to find the triangle's:
  • vertical length
  • horizontal length
• work out the vertical length ÷ horizontal length
• the result is the gradient of the line

The following graph shows the exchange rate for euros € and United States dollars $ in March 2011.

There are two marked points at (0, 0) and (70, 98).
By working out the gradient of the graph, we can find the exchange rate from euros to United States dollars.

• The vertical distance between (0, 0) and (70, 98) is 98.
• The horizontal distance between (0, 0) and (70, 98) is 70.
• 98 ÷ 70 = 1.4

This means that 1 euro is equal to 1.4 United States dollars.