Prove that for any natural number there is a multiple of it, the decimal notation of which consists of only 0 and 1.
Without calculating the answer to \(2^{30}\), prove that it contains at least two identical digits.
Write the following rational numbers in the form of decimal fractions: a) \(\frac {1}{7}\); b) \(\frac {2}{7}\); c) \(\frac{1}{14}\); d) \(\frac {1}{17}\).
Let the number \(\alpha\) be given by the decimal:
a) \(0.101001000100001000001 \dots\);
b) \(0.123456789101112131415 \dots\).
Will this number be rational?
Prove that in any infinite decimal fraction you can rearrange the numbers so that the resulting fraction becomes a rational number.
Prove that there are infinitely many composite numbers among the numbers \(\lfloor 2^k \sqrt{2}\rfloor\) (\(k = 0, 1, \dots\)).
Prove the irrationality of the following numbers:
a) \(\sqrt{3}{17}\)
b) \(\sqrt{2} + \sqrt{3}\)
c) \(\sqrt{2} + \sqrt{3} + \sqrt{5}\)
d) \(\sqrt{3}{3} - \sqrt{2}\)
e) \(\cos 10^{\circ}\)
f) \(\tan 10^{\circ}\)
g) \(\sin 1^{\circ}\)
h) \(\log_{2}3\)
Is it possible for
a) the sum of two rational numbers irrational?
b) the sum of two irrational numbers rational?
c) an irrational number with an irrational degree to be rational?
One of the roots of the equation \(x^2 + ax + b = 0\) is \(1 + \sqrt 3\). Find \(a\) and \(b\) if you know that they are rational.
Prove that the number \(\sqrt {2} + \sqrt {3} + \sqrt {5} + \sqrt {7} + \sqrt {11} + \sqrt {13} + \sqrt {17}\) is irrational.