Answer:
See explanation
Step-by-step explanation:
If then triangle PXY is isosceles triangle. Angles adjacent to the base XY of an isosceles triangle PXY are congruent, so
and
Angles 1 and 3 are supplementary, so
Angles 2 and 4 are supplementary, so
By substitution property,
Hence,
Consider triangles APX and BPY. In these triangles:
- - given;
- - given;
- - proven,
so by ASA postulate.
Congruent triangles have congruent corresponding sides, then
Therefore, triangle APB is isosceles triangle (by definition).