You only need two points to describe a linear equation because there are only two unknowns from y=mx+b, namely m, the slope and b the constant or y-intercept.
You can find the slope by finding the change in y divided by the change in x from any two points...here I'll use (0,5) and (1,3)...so the slope or m is:
m=(dy/dx)=(3-5)/(1-0)=-2 now are line so far is:
y=-2x+b and we can use any point now to solve for be, I'll again use (1,3)
3=-2(1)+b
3=-2+b
5=b now we have solved for both m and b our line is:
y=-2x+5