Which pair of triangles must be similar?



Triangle 5 has a 30∘ angle and a 90∘ angle. Triangle 6 has a 30∘ angle and a 70∘ angle.

Triangles 1 and 2 each have a 35∘ angle.

Triangle 7 has a 50∘ angle and a 25∘ angle. Triangle 8 has a 50∘ angle and a 105∘ angle.

Triangles 3 and 4 are both isosceles. They each have a 40∘ angle.