My screen broke,can I still use an external t.v?

Yes, since the video card of the laptop should still be working. (the video card is ultimately responsible for outputting to both the built-in display and external displays, and won't be hurt if the screen broke.) The tricky part comes with the settings - some computers will automatically switch to either mirror or extended mode when you connect the laptop to the TV. When I had to do this for my Sister after she dropped an alarm clock on her screen, I ended up having to use key shortcuts to open the display settings, then fish the window onto the other display to set it to mirror.

I'm assuming the laptop has HDMI? Go ahead and plug it into your tv, making sure your laptop is plugged into its charger. Once its connected to the tv and the tv is on the right source, close the laptop lid. If all goes well, it should treat the TV as the main desktop once the laptop lid is closed.

If closing the lid didn't work, and it displays in extended, you'll need to do Windows+R to open the run app, then type in control panel and press enter. I believe you should be able to do this without the laptop's display. After that, you'll have to fish for the window and drag it over to the tv to switch to mirrored desktop.

Hope this helps!

- Ben