# irrational numbers

• January 27th 2011, 03:51 AM
fxs12
irrational numbers
prove that the following are irrational numbers

1) tan 5

2) log 6 to the base 7
• January 27th 2011, 04:39 AM
Soroban
Hello, fxs12!

Here's the second one . . .

Quote:

$\text{Prove that the following are irrational numbers: }$

. . $(1)\;\tan 5 \qquad\qquad (2)\;\log_76$

Suppose $\log_76$ is rational.

Then: . $\log_76 \:=\:\dfrac{n}{d}\:\text{ for some integers }n,d$

. . And we have: . $7^{\frac{n}{d}} \:=\:6$

Raise both sides to the power $\,d\!:\;\;7^n \:=\:6^d
$

. . And we have: . $7^n \;=\;2^d\cdot3^d$

We have a number that has two distinct prime factorizations.
This is contradiction of the Fundamental Theorem of Arithmetic.

Therefore: . $\log_76$ is irrational.

• January 28th 2011, 12:33 AM
mr fantastic
Quote:

Originally Posted by fxs12
prove that the following are irrational numbers

1) tan 5

[snip]

Since $\tan (n \theta^{0})$ is a rational function of $\tan (\theta)$ it can be deduced from the fact that $\tan 60^{0} = \sqrt{3}$ that $\tan (n^{0})$ is irrational for n = 1, 2, 3, 4, 5, 6, 10, 12, 15 or 30.
• January 28th 2011, 12:49 AM
Prove It
Is this $\displaystyle \tan{(5^{\circ})}$ or $\displaystyle \tan{(5^C)}$?