In an isosceles triangle, the outer angle at the base is 140, find the larger angle of this triangle.

1) If the outer angle of an isosceles triangle is 140 °, then the angle at the base (inner) will be:

180 – 140 = 40 °, because the sum of the outer and inner angles of the triangles is 180 °.

2) Since the triangle is isosceles, the angles at the base are equal, therefore the second angle of the base is also equal to 40 °.

3) Find a large angle:

180 – 40 – 40 = 100 °.

Answer: The large angle of the triangle is 100 °.