sorry for reposting but i need an answer
how would you write 565 nm as a decimal
how would you write 590 nm as a decimal
How you rewrite 565 nm depends upon what units you want to use. If you want the number to be less than 1, you could express it in centimeters or meters.
For example, 565*10^-9 m = 0.00000000565 meters
Few people would want to write it that way. They would use nanometers or scientific notation.
Similary for your other number.