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What makes the speed of light exactly 299,792,458 metres per second?

Answer 1

The definition of the metre.

The definition of a metre used to be the length of a specific International Prototype Metre, which was a platinum-iridium metal bar measured at the melting point of ice.

In #1960#, the standard was changed to be expressed in terms of wavelengths of the red-orange spectral line of Krypton-86.

In #1983#, the definition was updated to be exactly #1/299792458# the distance travelled by light in vacuum in one second.

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Answer 2

Everett Abrams

According to international agreement, the speed of light, represented by the letter "c," is 299,792,458 meters per second. This value is derived from measurements of the constant speed of light in a vacuum.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.