How do i do this i do not understand it

"Complete the equation of the line through (2, 1) and (5, -8). Use exact numbers."

This is how you solve it.
First, you need to find the slope. The slope formula is... y2 - y1

x2 - x1
Coordinates: (2, 1) and (5, -8)
x1, y1 x2, y2

Plug the numbers in to get...

-8 - 1 -9
=
5 - 2 3

Slope: -3 (Keep in mind the equation is y=mx+b and slope=m)

Now for the y - intercept.

Pick a point.
y=mx+b
Replace y with y in point you picked, in the case I'll pick (2, 1)
x y
1=(slope)
1= -3 times (x)
1= -3(2) + b (we are trying to find that right now)
Now it's just a one step equation
1= -6 + b (Rid of six since you cancelled it out)
+6 +6
7= b (7 is your b or your y - intercept)

Put it all together to get y= -3x + 7

Happy Thanksgiving, I hope this helps for all future problems!

"Complete the equation of the line through (2, 1) and (5, -8). Use exact numbers."

This is how you solve it.
First, you need to find the slope. The slope formula is... y2 - y1

x2 - x1
Coordinates: (2, 1) and (5, -8)
x1, y1 x2, y2

Plug the numbers in to get...

-8 - 1 -9
=
5 - 2 3

Slope: -3 (Keep in mind the equation is y=mx+b and slope=m)

Now for the y - intercept.

Pick a point.
y=mx+b
Replace y with y in point you picked, in the case I'll pick (2, 1)
x y
1=(slope)
1= -3 times (x)
1= -3(2) + b (we are trying to find that right now)
Now it's just a one step equation
1= -6 + b (Rid of six since you cancelled it out)
+6 +6
7= b (7 is your b or your y - intercept)

Put it all together to get y= -3x + 7

Happy Thanksgiving, I hope this helps for all future problems!