#f(x)=-4x#
Substitute #y# for #f(x)#.
#y=-4x# is in the slope-intercept form of a linear equation #y=mx+b#, where #m# is the slope, and #b# is the y-intercept.
For #y=-4x,# #m=-4#, and #b=0#.
To find points on the line, substitute values for #x# and solve for #y#.
Determine the value of #y# if #x=0#.
#y=-4(0)=0#
So the point in which #x=0# is #(0,0)#.
To find a second point, substitute another value for #x#.
#x=1,# #y=-4#
So now we have two points, #(0,0)# and #(1,-4)#, that we can plot and then draw a straight line through the two points.
Alternatively, you can use the slope of #-4# to determine other points. You could start at the origin #(0,0)#, and move #4# places down the y-axis, then move to the right #1# place to the point #(1,-4)# Conversely, you could move #4# places up the y-axis and #1# place to the left to get the point (#-1,4)#. You can plot those points and draw a straight line through them.
graph{y=-4x [-10, 10, -5, 5]}
