Show why when using the sieve method to find all primes less

Show why, when using the sieve method to find all primes less than n, you need only strike out multiples of the primes whose square is less than or equal to n. 3.

Solution

ANSWER :-

Suppose to the contrary n= ab

where a,b > sqrt(n)

Then, n = ab > sqrt(n) * sqrt(n) = n

This is a contradiction.