In: Advanced Math
Use the method of exhaustion to prove the following statement: “For every prime number p between 30 and 58, 10 does not divide p − 9.”
Prove that 0.17461461 . . . is rational (digits 461 in the fractional part are periodically repeated forever).
First question:
Primes between and are
These are primes because and has no divisor other than (neither of divides ) implies is a prime, and has no divisor other than (neither of divides ) implies is a prime, and has no divisor other than (neither of divides ) implies is a prime, and has no divisor other than (neither of divides ) implies is a prime, and has no divisor other than (neither of divides 47) implies 47 is a prime, and has no divisor other than (neither of divides ) implies is a prime.
Now, for , we have
and divides none of . This proves the desired statement.
Second question:
We have
The series in the parenthesis is a geometric series with common ratio
Therefore,
which is a rational number.