The first is a right triangle because there is a right angle, and it is scalene because none of the sides are congruent.
The second is an obtuse triangle because there is an obtuse angle, and it is an isosceles triangle because two of the sides are congruent.
The third is an acute triangle because all of the angles are acute, and it is an isosceles triangle because two of the sides are congruent.
The fourth is a right triangle because it has a right angle, and it is a scalene because none of the sides are congruent.
