Answer:
16 is right, 17 is acute, 18 is obtuse
16, the angles that are touching each other and meet at the right angle (the square in the corner) are congruent, all are congruent on 17, and the two that aren't super long are congruent on 18
Explanation:
Congruent means that they're the same length, and I kind of assumed on some of them, so yeah.
16: The square in the corner means a right angle, so that tells us it's a right triangle. This is the type of triangle that uses the equation a^2+b^2=c^2. C, or the hypotenuse, or the one that isn't part of the right angle, will always be longer than the other two.
17: An acute triangle is one where none of the corners are larger than 90*. This is one where I assumed on the lengths. So, that part may be wrong. But...., it may be one of those really nice acute triangles where all of the corners are 60*, which would make me right.
18. Obtuse triangles are the ones with a corner larger than 90*. This triangle clearly has one. And, one side is obviously longer than the others, so the others appear to be the same length.