so I'm given 

```
y' = sec(t)/tan(t)
   = 1/sin(t)

```

I'm then asked to find the derivative of this, and in the example it shows 

```
d/dt y' = d/dt (1/sin(t))
        = -cos(t)/sin^2(t)

```

and I have absolutely no idea how they got that last line, could anyone help me out?

Thanks