Hello, P S.,
Slope intercept form is y = mx + b, where m is the slope and b is the y-intercept (where the line passes through the y axis at x = 0).
The slope is defined as the rise over the run (rise/run) of the equation. It literally means that if you take the two points provided, you can calculate the "run," which is the distance travelled along the x axis from left to right. For (-5, 19) and (5, 13), the run would be 5 + 5 = 10 (you need the absolute value of -5 to get the distance). Another way to do this is to take the right hand value (5) and subtract the starting value (-5) to arrive at the same answer, 10. That is the "run." The rise is how much the y value changes over the same change in x. Here, we take the (5, 13) and subtract the 19 from the 13, to get -6 for the rise. (A minus means it drops as x increases). So the slope is -6/10, or -0.6.
We can put that into the equation to make it y = -0.6x + b.
We need to find b, so let's put in the values of x and y of the provided points the line crosses. Since these points satisfy the line equation, we can use them to calculate b.
For (-5, 19), we get: 19 = -0.6*(-5) + b
19 = 3 + b, b = 16
This would mean y = -0.6x + 16 is the line we are seeking.
To double check, use the other data set of (5, 13) and see if it works:
13 = -0.6(5) + 16 ??? 13 = -3 + 16; 16 = 16: YES
y = -0.6x + 16, with points (-5, 19) and (5, 13) noted. (Each chart line is 2.)
Bob