hey buddy the derivation part is :

the relation between frequency and time period :
let the time take for oscillation = 1 s
time take for one oscillation = (1/nu)s

but the time taken for one oscillation is called the time period (T) and the number od oscillation per second is called frequency (nu)

hence frequency and time period are related as T = 1/nu or nu = 1/T

here in this derivation s = seconds
nu = its a Greek word which is used for denoting frequency
2 5 2
hey buddy will this part be enough ? or should i write something more in it ?
Both are inversely proportional to each other