Question

Which triangle is not congruent to the other three triangles?

Answer 1

For all four triangles, we have the angles 50°, 60° and 70°, and one side with length equal 9.

In the options b, c and d, the side measuring 9 is between the angles 50° and 60°, but for option a, this side is between the angles 50° and 70°, so it's a different side, therefore the triangle is not congruent.

So the correct option is 'a'.