The outer angle at the base of an isosceles triangle is 135 °. Determine the type of triangle (at the corners).

Recall that the sum of adjacent angles is 180 °. So we can find the value of one of the inner angles of the triangle:
180 – 135 = 45 °;
By condition, the triangle is isosceles, which means that the side angles in this triangle are equal.
This means that the second angle of the triangle will also be 45 °.
Now we can find the third corner and draw a conclusion about what this triangle will be:
180 – 45 – 45 = 90 ° is the third angle;
90 ° is a right angle, so the triangle will be rectangular.
Answer: right triangle