One of the equal angles of an isosceles triangle is 50°. Find all the angles of this triangle.

Let the there angles be $\angle$x, $\angle$y  and $\angle$z.

∠y = ∠z = 50° (Angle opposite to equal sides of a triangle are equal)
$\angle$x + 50° + 50° = 180° (Angle sum property of a triangle)
⇒ ∠x + 100° = 180°
⇒ ∠x = 180° – 100° = 80°
$\therefore$ ∠x = 80°