Hoi!
The converse of the Pythagorean Theorem states that if the square of the length of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is right.
To determine if this is a right triangle, let's figure out the values of each side.
√36 = 6
√18 = 4.2
Now we use the formula a² + b² = c² to determine if this is a right triangle.
4.2² + 4.2² = 6²
18 + 18 = 36
36 = 36
This triangle is a right triangle, so your answer is True.