To add points to an existing plot, use `points()`

```
n = 50
set.seed(0)
x = sort(runif(n, min=-2, max=2))
y = x^3 + rnorm(n)
plot(x, y)
points(x, x^3, pch=20, col="red")
```

To add lines to an existing plot, use `lines()`

```
plot(x, y)
lines(x, x^3, col="red")
```

`points()`

and `lines()`

can be called multiple timesThese functions can be called repeatedly, to continue adding to the current plotting window

```
plot(x, y)
lines(x, x^3, col=2)
lines(x, x^3 + qnorm(0.90), col=3)
lines(x, x^3 + qnorm(0.10), col=4)
```

To add a line of the form \(y = a+bx\) to an existing plot, use `abline()`

. Can also add vertical or horizontal lines. Lastly, can set line type, width, and color, as usual

```
plot(x, y)
abline(a=0, b=3)
abline(h=0, lty=2, lwd=3, col="red")
```