# 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.

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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.

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Law of cosines:
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Law of sines:
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Law of tangents:
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*
Area formulas:
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*
Radii of circumscribed and inscribed circles:
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