① The two acute angles of a right triangle are complementary angles.

② The median line on the hypotenuse of a right triangle is equal to half of the hypotenuse.

③ The sum of squares of two right angles of a right triangle is equal to the square of the hypotenuse (Pythagorean theorem).

(4) In a right triangle, a right angle of 30 degrees is equal to half of the hypotenuse. ?

Determination of right triangle;

A triangle with two complementary angles is a right triangle.

(2) If the three sides of triangle A, B and C have the following relationship A 2+B 2 = C 2, then this triangle is a right triangle (the inverse theorem of Pythagorean theorem). ?

The above explanation and study of the right triangle theorem formula in mathematics can be well mastered by students, and I hope all students can get in.

The nature of isosceles triangle;

① The two base angles of an isosceles triangle are equal.

② The bisector of the top angle of the isosceles triangle, the median line on the bottom edge and the height on the bottom edge coincide (the three lines are one).

Trilateral relation theorem and inference of triangle: the sum of two sides of triangle is greater than the third side, and the difference between the two sides is less than the third side.

Theorem of sum of interior angles of triangle: the sum of three interior angles of triangle is equal to 180 degrees.

Theorem of sum of external angles of triangle: one external angle of triangle is equal to the sum of two non-adjacent external angles.

External Angle of Triangle and Theorem Reasoning: The external angle of a triangle is greater than any internal angle that is not adjacent to it.

The bisectors of three angles of a triangle intersect at a point (center).

Perpendicular bisector of three sides of a triangle intersect at one point (outer center).