Option C:
Right triangle
Solution:
To find what kind of triangle is ΔACD.
Option A: Obtuse triangle
If any one of the angle in a triangle is more than 90°, then the triangle is obtuse triangle.
The angles in the given triangle ACD are not more than 90°.
So, the given triangle is not obtuse triangle.
Option B: Isosceles triangle
If any two sides of the triangle are equal, then the triangle is isosceles triangle.
The sides in the given triangle ACD are not equal.
So, the given triangle is not isosceles triangle.
Option C: Right triangle
If any one of the angle in a triangle is exactly 90°, then the triangle is right triangle.
In the ΔACD, angle A = 90°.
Therefore, ΔACD is right triangle.
Option D: Equilateral triangle
If all the three sides and all the three angles are equal, then the triangle is an equilateral triangle.
In ΔACD, not all the angles are equal.
Therefore , it is not an equilateral triangle.
Option C is the correct answer.
Hence ΔACD is a right triangle.