# Basic relations between elements of triangle

*Law of cosines. Law of sines. Law of tangents.*

Area formulas. Heron’s formula.

Radii of circumscribed and inscribed circles.

Area formulas. Heron’s formula.

Radii of circumscribed and inscribed circles.

*Designations:**a*,* b*,* c* – sides; *A*, *B*, *C* – angles of triangle;

*p* = ( *a + b + c* ) / 2 – a half-perimeter; *h – *a height; *S* – an area; *R*,* r* – radii of circumscribed

and inscribed circles correspondingly.

*Law of cosines:*

*Law of sines:*

*Law of tangents:*

* Area formulas:*

*Radii of circumscribed and inscribed circles:*