Explanation:
so (2,1) (1,3)
x1,y1 x2,y2
so then it would be
the slope is -1
so the equation is after using your x1 and y1 would be
y-1=-1(x-2)
and after you solve that by using the comunitive property, then it will look like
y-1=-1x+2
then you subtract 1 from the y side and make it
the answer is y=-1x+3