First, you should know what the format for point slope form is. y-y1=m(x-x1). Now, fill in the points to the x1 and y1 variables. It doesn't matter what ordered pair you use. If the number you fill in is negative, for example, -1, change it to a positive 1. If you're plugging in a positive number such as 9, it becomes -9. Now, it may look like this: y-9=m(x+1). However, you still need to find slope. You can use the expression y-y1/x-x1. 9-1=8. -1-1= -2. So, your slope is 8/-2. However, you can simplify this to -4. Now, plug in -4 to your equation to have your final answer: y-9=-4(x+1).
