133. In an isosceles triangle, one of the angles is $80^{\circ}$. What are its other angles? (List all possibilities.)
$\triangleright$ In an isosceles triangle, the two angles at the base are equal. If one of them is $80^{\circ}$, then together they sum up to $160^{\circ}$, and the third angle (at the vertex) is left with $20^{\circ}$. If, however, the angle at the vertex is $80^{\circ}$, then the two angles at the base are left with $100^{\circ}$, and each of them is $50^{\circ} . \triangleleft$