Sine and Cosine Law
Each side of a triangle is directly proportional to the sine of the opposite angle.
In a triangle the square of every side is equal to the sum of the squares of the other two less the double product of the product of both for the cosine of the angle that they form.
Law of Tangents
Area of a Triangle
The area of a triangle is half the product of the base and the height.
The area of a triangle is half the product of two sides by the sine of the angle that they form.
The area of a triangle is the quotient between the product of its sides and four times the radius of its circumscribed circle.
The area of a triangle is equal to the product of the radius of the inscribed circle by the semiperimeter.