Answer:
For #17:
This is a 45-45-90 triangle. Therefore, the missing side length (x) is equal to the other leg of the triangle, which is 6.
For #18:
This is a 30-60-90 triangle. Therefore, the missing side length (m) is equal to the hypotenuse (18) divided by 2, or 9.
For #19:
This is a 30-60-90 triangle. Therefore, the missing side length (y) is equal to the hypotenuse (12) multiplied by the square root of 3, or 12√3.
For #20:
This is a 30-60-90 triangle. Therefore, the missing side length (u) is equal to the short leg (5√3) multiplied by 2, or 10√3.
For #21:
This is not a right triangle because the angles do not add up to 180 degrees.
For #22:
This is a right triangle because the angles add up to 180 degrees and one of the angles is 90 degrees.
Explanation: