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1.
$1^\prime=\dfrac{\pi}{180 \cdot 3600}\,\text{rad}\approx 0.000291\text{rad}$
2.
$1^{\prime\prime}=\dfrac{\pi}{180 \cdot 3600}\,\text{rad}\approx0.000005\,\text{red}$
3.
$\sin^2\alpha+\cos^2\alpha=1$
4.
$\tan\alpha=\dfrac{\sin\alpha}{\cos\alpha}$
5.
$\cot\alpha=\dfrac{\cos\alpha}{\sin\alpha}$
6.
$\tan\alpha\cdot\cot\alpha=1$
7.
$\tan^2\alpha=\dfrac{1}{\cos^2\alpha}-1$
8.
Sine of sum of angles
$\sin(\alpha+\beta)=\sin\alpha \, \cos\beta + \sin\beta \, \cos\alpha$
9.
$\sin(\alpha - \beta) = \sin\alpha \, \cos\beta - \sin\beta\,\cos\alpha$
10.
$\cos(\alpha+\beta)=\cos\alpha\cos\beta-\sin\alpha\sin\beta$
11.
$\cos(\alpha-\beta)=\cos\alpha\cos\beta+\sin\alpha\sin\beta$
12.
$\tan(\alpha+\beta)=\dfrac{\tan\alpha + \tan\beta}{1-\tan\alpha\tan\beta}$
13.
$\tan(\alpha-\beta)=\dfrac{\tan\alpha - \tan\beta}{1+\tan\alpha\tan\beta}$
14.
$\cot(\alpha+\beta)=\dfrac{1-\tan\alpha\tan\beta}{\tan\alpha+\tan\beta}$
15.
$\cot(\alpha-\beta)=\dfrac{1+\tan\alpha\tan\beta}{\tan\alpha-\tan\beta}$
16.
Difference of fifth powers
$a^5-b^5=(a-b)(a^4+a^3b+a^2b^2+ab^3+b^4)$
17.
Sum of fifth powers
$a^5+b^5=(a+b)(a^4-a^3b+a^2b^2-ab^3+b^4)$
18.
Square of difference
$(a-b)^2=a^2-2ab+b^2$
19.
Square of sum
$(a+b)^2=a^2+2ab+b^2$
20.
Cube of difference
$(a-b)^3=a^3-3a^2b+3ab^2-b^3$