Outside angle of triangle 40 find the angles of triangle ABC if AB = BC

From the condition we know that the outer angle of an isosceles triangle is 40 °. In order to find the interior angles, we will use the property of the adjacent angles of the triangle.

Let’s remember it. Adjacent angles of a triangle add up to 180 °.

Using this, we can find the corner of the triangle adjacent to the outer corner.

180 ° – 40 ° = 140 °.

We also know the theorem that the sum of the angles of a triangle is 180 ° and that the angles at the base of an isosceles triangle are equal.

180 ° – 140 ° = 40 °.

40 °: 2 = 20 °.

Answer: 140 °; 20 °; 20 °.