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.