Isosceles Triangle: Finding Angle X When Base Angle is 55 Degrees

Question

ABC is an isosceles triangle.

AB = AC

Angle B equals 55 degrees.

Find the value X.

00:00 Find X

00:06 An isosceles triangle according to the given data

00:09 Base angles are equal in an isosceles triangle

00:19 The sum of angles in a triangle equals 180

00:25 Therefore it is the complementary angle to 180

00:35 Let's substitute appropriate values according to the given data and solve for the angle

00:41 This is angle BAC

00:48 Vertical angles are equal

00:51 And this is the solution to the problem

Since this is an isosceles triangle, angle B and angle C are equal to each other.

$B=C=55$

Therefore we can calculate angle A since the sum of the angles in the triangle equals 180:

$A=180-55-55=180-110=70$

Since angle X is the vertex of angle A, they are equal, hence:

$A=X=70$

$70$