I have a few doubts in here

#1

like how van B=a(p-1)+b and hows b=B/p-1

#2

also why didnt we directly did B%p like we did with A

#3

@chemant077 Suppose have a number x and y now let me write some statements.
x/y=k (quotient)
x%y=r (remainder)
Now you can easily see that (basic maths)
x= ky + r
x= ky + x%y
Now in the given question .
B= a*(p-1) + b
If we compare the above equation with the one I derived you can easily understand how we get B (here (p-1) is divisor)
so
B%(p-1)=b (rem)
B/(p-1)=a (quotient)
We choose to factor B in terms of p-1 instead of p, so as to utilize the property . (x^(m-1))%m=1 (m is prime)
If this resolves your doubt mark it as resolved.

#4

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