slope intercept form is y=mx+b
first plug in m
y=-1/2X + b
now plug in the point (8,1) for the x and the y
1=-1/2(8) + b
now you need to solve for b
simplify
1=-4+ b
add 4
5=b
now that you know b
you can plug it into the equation along with the m
so the answer is
y=-1/2X + 5
