The equation 13x+8y=128 can be graphed. Would the point (5,8) fall below, on, or above the graph? How would you know without graphing it?

Question

Please remember to include all necessary information justifying your answer

Answer 1

Hi Zakiya, you can actually find out the answer without graphing. Here's how:

 

Find the y value of the above equation for x=5

 

=> 13(5) + 8y = 128

 

<=> 13(5) + 8y - 13(5)= 128 - 13(5)

 

<=> 8y = 128 - 13(5)

 

<=> 8y/8 = [128 - 13(5)]/8

 

<=> y = [128 - 13(5)]/8

 

=> y = 7.875 < 8

 

As you can see the y value of the equation of the line (7.875) is less than the y value of the point (8). Therefore, the point falls above the graph.

 

I hope this helps