hi,
a point is given ( x; y)
standar line equation is : y = ax+b
So with (3;5) and (8;15) we have :
3a+b = 5
8a+b = 15
so :
8a+b - ( 3a +b) = 15 -5
8a +b -3a -b = 10
8a-3a = 10
5a = 10
a = 10/5
a = 2
if a = 2 so 3*2 +b = 5
6+b = 5
b = 5-6
b = -1
so let check :
8*2 + (-1) = 16 -1 = 15
and 3*2 -1 = 6-1 = 5
coordonnate works for both point, so line is y = 2x -1
