If the vertex angle of an isosceles triangle is 50 degrees, find the number of degrees in one of the base angles.

Question

Hi! I'm completely lost. If someon could help me that would be great!

Here were ten given choices:

A: 50

B:130

C:60

D:65

E:55

Answer 1

The Answer is D 

The base angles of an isosceles triangle are equal 

and their sum is equal to 130 because the sum of the angles of a triangle is 180. the vertex angle is 50 so 180 - 50 = 130.

since the base angles are equal. then divide 130 by 2 so you have 65 which is D.

Answer 2

Lets think it through.

What do I know FOR SURE about this triangle?

1) That it is isosceles. That means two angles are equal, and one is different.

2) I also know that the base angles are always the same, and the vertex is the angle that is different.

             (Imagine the triangle standing like an upside down ice cream cone. Then imagine it lying on its side. If the                     base angles would be different from each other, the whole shape would be lopsided.)

3) My vertex (top) angle is fifty degrees.

4) ALL triangle are 180 degrees.

5) 180-50=130 My two unknown angle equal 130 degrees together.

    They are equal, so we can divide these 130 degrees into 2 equal parts

    130/2=65 Each base angle is 65 degrees.

 

Good luck!