How do you find the slope of (4,5) and (9,-10)?

1 Answer
MeneerNask
Feb 3, 2015

Slope is defined as the difference in #y# per unit #x#

As we don't have units here, we divide the change in #y# by the change in #x#, or in formula (#Delta# means change):
Slope= #(Deltay)/(Deltax)=(y_2-y_1)/(x_2-x_1)=(-10-5)/(9-4)=(-15)/5=-3#

Now we're at it we can also define the whole equation:

Just put in the numbers for one of the points:
#y=ax+b->5=-3*4+b->b=17#
So the equation will be: #y=-3x+17#
graph{-3x+17 [-44.86, 59.17, -26.06, 25.96]}
And you can check your answer against the other point:
#-3x+17=-3*9+17=-10# which is correct.

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