The equation of the line below can be expressed in the form
\frac{x}{a} + \frac{y}{b} = 1.
Find a.
The lines passes through (5,8) and (-4,17).
Find slope between the two points m = (y1-y2) / (x1-x2)
m = (8-17) / ( 5 - -4) = -9/9 = - 1
Point slope form is then (pick either point)
y-8 = -1 (x-5)
re-arrange
y-8 = - x + 5
x + y = 13 Divide by 13
1/13 x + 1/13 y = 1 then a = 13 Done.