Question

How can we proove that speed of light is 3 × 10^8 m/s

Answer 1

WE CAN PROVE THE SPEED OF LIGHT...
BY THE DISTANCE FROM SUN TO EARTH...
WHICH IS 1 ASTRONOMICAL UNIT...
AND IT TAKES 8 MINS . FOR LIGHT TO COME ON EARTH

Answer 2

The speed of light in a vacuum stands at “exactly 299,792,458 metres per second“. The reason today we can put an exact figure on it is because thespeed of light in a vacuum is a universal constant that has been measured with lasers; and when an experiment involves lasers, it's hard to argue with the results