If an external angle of an isosceles triangle is known to be 120 degrees, then it is () A. Isosceles right triangle B. general isosceles triangle C. equilateral triangle D. isosceles obtuse triangle

If an external angle of an isosceles triangle is known to be 120 degrees, then it is () A. Isosceles right triangle B. general isosceles triangle C. equilateral triangle D. isosceles obtuse triangle

① If the angle of 120 ° is the outer angle of the apex angle, the apex angle is 180 ° - 120 ° = 60 ° and the base angle is (180 ° - 60 °) △ 2 = 60 ° and the triangle is an equilateral triangle; ② if the angle of 120 ° is the outer angle of the base angle, the base angle is 180 ° - 120 ° = 60 ° and the apex angle is 180 ° - 60 ° × 2 = 60 ° and the triangle is an equilateral triangle

If the waist length of an isosceles triangle is 2cm and the area is 1cm & sup2;, then its vertex degree is?

The height of a waist is h = 2S / a = (2 × 1) × 2 = 1 (CM)
Then the vertex angle is 30 degrees (the right side opposite 30 degrees is equal to half of the hypotenuse)

Isosceles triangle waist length is 12, area is 36, what is the vertex angle

0.5×12×12×sina=36
sina=0.5
So a = 30 degrees

If the waist length of an isosceles triangle is 10 cm and the area is 25 square cm, then the degree of the vertex angle is?

If the degree of vertex angle is x and a height is made on any waist of the triangle, then:
Let the length of the height be h, so SiNx = H / 10, that is, H = 10 * SiNx,
And because its area is 25, so
25=（10*H）/2
By substituting the above formula h, we get
25＝（10*10*sinX）/2
The result shows that SiNx = 1 / 2
So the degree of vertex angle X is 30 degrees
thank you!