Drawing a straight line graph using the intercept method

Introduction

Good day grade 9 class. Today we will be drawing and plotting a graph using the dual intercept method, with the equation of y=mx+c.

Points to keep in mind from the previous topic ( finding the gradient).

  • In the equation y=mx+c, the letter m represents the gradient and the letter c represents the y intercept.
  • The letter c is also the point where the line on the graph crosses the y axis.

Recourses needed for this lesson:

pen, pencil, ruler, graph paper, scientific calculator

Task

Given the equation y= 2x-5 

  1. Find the x intercept 
  2. Find the y intercept
  3. Draw and plot the graph

Process

Given the equation y = 2x - 5 

  1. Find the x intercept
  • Step 1: In order to find the x intercept let the y value in the equation = 0
  • Step 2 : Substitute the 0 into the equation.

                      y = 2x - 5

                     (0)= 2x - 5 (carry the -5 over and it changes into a +)

                      5 = 2x (In order to get x on its own, dive both sides by 2)

                   5/2 = 2x/2 (both 2's cancel each other out)

                  2,5 = x 

                 so therefore x =2,5

 The coordinates is (0; 2,5)     

       2. Find the y intercept

  • Step 1: In order to find the y intercept let the x value in the equation = 0
  • Step 2 : Substitute the 0 into the equation.

                      y = 2x - 5

                      y = 2 (0) - 5

so therefore   y = -5

The coordinates is (-5; 0)

So now that we have 2 coordinates of the graph y=2x-5 we can plot it on the graph

 

 

 

Evaluation

Now try these few examples on your own.

y = -3x + 6

y = -x - 2

  1. Find both the x and y intercept using the dual intercept method for both graphs.
  2. Plot both graphs on the same cartesian plain. 
  3. Name the lines on the graph y = -3x + 6 (Graph A) y = -x - 2 (Graph B)

Use the link attached below to check if your graph has been drawn and plotted correctly.

https://www.youtube.com/watch?v=MehFZ_1FPAM

Conclusion

In conclusion to the lesson today, here are some links shows more examples that can be followed to find the x and y intercept using the dual intercept method.

https://www.youtube.com/watch?v=6m642-2D3V4

https://www.youtube.com/watch?v=ykZe9pNy4JA

The link below is an exercise for you to complete on your own.

  • Keep in mind that all calculations should be shown.
  • Use the dual intercept method
  • Have fun and good luck!

https://www.bossmaths.com/wp-content/uploads/A9a2s.009.jpeg

 

Credits

Everything done by M Hattas