,
y = x
(m = 1,   c = 0)
y = 
3 x
(m = 
3 ,  c = 0)
y = x + 1
(m = 1,  c = 1)
y = – x
(m = – 1,  c = 0)
y = – x – 1
(m = – 1,  c = – 1) etc ( see Fig 9 2) Thus, equation (5) represents the family of straight lines, where m, c are parameters