I. Helen formula
Helen formula is a formula for calculating the side length of a triangle according to its perimeter and half perimeter. Assuming that the lengths of the three sides of a triangle are A, B and C, respectively, and the semi-circumference s=(a+b+c)/2, the area of the triangle can be obtained by Helen's formula: area =sqrt(s*(s-a)(s-b)(s-c)).
This formula can be used not only to calculate the area of a triangle, but also to solve the side length of a triangle when the angles of two sides of the triangle or three angles of the triangle are known.
Second, Pythagoras theorem
Pythagoras theorem is a formula to calculate the third side according to the angle between two sides of a triangle. This formula is based on the cosine theorem of triangles, that is, for any triangle ABC, there is an a 2 = b 2+c 2-2bc * COSA, where A, B and C are three sides of the triangle ABC respectively, and A is the included angle of angle A. ..
Through Pythagoras theorem, we can determine the length of the third side of a triangle, especially when the two sides and the included angle are known.
Third, Pythagorean theorem
Pythagorean theorem is a special case of right triangle, and the length of three sides is determined by the relationship between two right sides and hypotenuse of right triangle. Specifically, for any right-angled triangle, the sum of squares of right-angled sides is equal to the square of hypotenuse. This theorem is widely used in geometry, trigonometry, algebra and other fields.
Geometry, trigonometry and algebra
I. Geometry
The branch of mathematics that studies the relationship between shape, size and space. It originated from ancient land survey and architectural design. Geometry includes plane geometry, solid geometry and analytic geometry, and mainly discusses the properties, classification and transformation of graphics.
Second, trigonometry.
The branch of mathematics that studies the sides and angles of triangles and their relationships. Trigonometry is based on trigonometry, which describes the proportional relationship between angles and sides. Trigonometry is widely used in navigation, surveying and engineering. For example, trigonometry can be used to calculate distance, determine direction and solve practical engineering problems.
Third, algebra.
The branch of mathematics that studies mathematical symbols and algebraic operations. Algebra includes concepts such as polynomial, matrix, group, ring and field, and mainly discusses the solution of algebraic equations and the structural properties of algebra. Algebra is widely used in mathematics and other fields, for example, algebraic knowledge is often needed to solve practical problems such as physics, engineering and economy.