Function y = m x + c represents a straight line cutting + y at acute angle to +x.
m = tanq is called slope of the line.
q = anticlockwise angle made by the line with + x axis.
m = +ve if line makes acute angle to +x.
m = 0 if line is horizontal.
m = – ve if line makes obtuse angle to +x.
c = +ve if line cuts +y.
c = – ve if line cuts -y.
c = 0 if line passes through origin.