Show that every positive odd integer is of the form (4q+1) or (4q+3), where q is some integer.
From the euclid's theorem,
a=bq+r where b is divisor q is quotient and r is the remainder and .
Let's assume value of b =4
then a=4q+r,
Since divisor is 4, the possible remainder for the condition are 0,1,2,3.
So the possible values of a are,
4q,4q+1,4q+2,4q+3
Since a is odd, a cannot be 4q and 4q+2 because both are divisible by 2.
So the final values of a are 4q+1 and 4q+3.
Hence all positive odd numbers are of the form 4q+1 and 4q+3.
Hence Proved.