# plot a sin function
# the x-axis should range from -pi to pi, the y-axis from -1 to 1
# add a horizontal line at y=0 and a vertical line at x=0 that run through the entire plot

# hint: you can create a vector that holds a lot (100 or more) of values ranging from -pi to pi
# and plot those and the x-axis and their sin() on the y-axis
# abline should do the trick with the vertical and horizontal lines