Seems like people are saying the formula is y=360-90-90-(180-x) to find that y=x, but assuming the 360 number comes from the interior angles of both triangles, that feels very odd to me. Can anyone explain how they would solve this, or at least where those angles came from?

In the big triangle: 90_1 + y +z = 180

In the small triangle 90_2 + x + z = 180

equate both equation and you get x = y

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