Final answer:
The quickest solution is to press the laptop's function key (often F4, F5, F7, or F8) in combination with the Fn key to (Option b) toggle the display to duplicate mode, which will mirror the laptop screen on the external display.
Step-by-step explanation:
The quickest way to make a laptop's external display show exactly what is on the laptop's screen, when it is set to Extended desktop, is to toggle the dual display function key. Most laptops have a function key (often labelled as F4, F5, F7 or F8) that toggles the display modes between extended, duplicate, and projector only. This key is typically identified with a symbol depicting two screens or a rectangular shape. By pressing the Fn key (Function key) in combination with the relevant function key, you can cycle through the display options to select duplicate or mirror mode, which shows the same content on both the laptop screen and the external display.