please keep up
m = [(1/2)(5/5) - (4/5)(2/2)] ÷ [(3/2)(5/5) - (1/5)(2/2)]
m = [(5/10) - (8/10)] ÷ [(15/10) - (2/10)]
m = (-3/10) ÷ (13/10)
m = -30/130
m = -3/13 ... m is the gradient.
using the format y = mx + c ... we already found m so now we'll find see using the point [4/5,1/5]
(1/5) = (-3/13)(4/5) + c
(1/5) = (-12/65) + c
(1/5) - (-12/65) = c
(1/5)(13/13) + (12/65) = c
(13/65) + (12/65) = c
25/65 = c
5/13 = c
finally the equation is y = (-3/13)x + (5/13)