The equation of the straight line when one of the coordinate points are known can be represented as y - y1 = m(x - x1) . These type of forms are known as point slope form. Equation of the straight line can also be calculated without the slope when two points (x1 , y1) and (x2 , y2) are given.
Let us consider the co-ordinate points (x1,y1) and (x2,y2) as (9,1) and (8,2), then
(Y - 1) / (2 - 1) = (X - 9) / (8 - 9)
(Y - 1) / 1 = (X - 9) / -1
- (Y - 1) = (X - 9)
(-Y + 1) = (X - 9)
X + Y - 10 = 0