The formula of isosceles triangle is 1. If the base of a triangle is a and the height is h, then S=ah/2.
2. Given three sides A, B and C of a triangle, then (Helen formula) (p=(a+b+c)/2),
S=sqrt[p(p-a)(p-b)(p-c)]
= sqrt[( 1/ 16)(a+b+c)(a+b-c)(a+c-b)(b+ c-a)]
= 1/4 sqrt[(a+b+c)(a+b-c)(a+c-b)(b+c-a)]
3. Given two sides A and B of a triangle, the included angle between the two sides is C, then S= 1/2absinC, that is, the product of the two sides is multiplied by the sine value of the included angle.
4. Let the three sides of a triangle be A, B and C respectively, and the radius of the inscribed circle be R, then the triangle area =(a+b+c)r/2.
5. Let the three sides of a triangle be A, B and C respectively, and the radius of the circumscribed circle be R, then the triangle area =abc/4R.
6. Remember the Pythagorean theorem of right triangle: a*a+b*b=c*c, where c is the length of the hypotenuse: c = a/sin (45) = a/(sqrt (2)/2) = sqrt (2) * a is about =1.4/kloc.
Definition of isosceles triangle: In the same triangle, two triangles with equal sides are isosceles triangles.
Decision Theorem: In the same triangle, if two angles are equal, then the opposite sides of the two angles are also equal (abbreviated as equilateral).
In addition to the above two basic methods, there are the following ways to judge:
In a triangle, if the bisector of an angle coincides with the median line of the opposite side of the angle, the triangle is an isosceles triangle and the angle is the vertex.
In a triangle, if the bisector of an angle coincides with the height of the opposite side of the angle, the triangle is an isosceles triangle and the angle is the vertex.
In a triangle, if the midline of one side coincides with the height of that side, then the triangle is an isosceles triangle, and that side is the base.