Which best explains why this triangle is or is not a right triangle?

It is a right triangle.

Step-by-step explanation:

By the  Inverse Pythagoras Theorem if 39^2 = 36^2 + 15^2  then it is a right triangle.

39^2 = 1521

36^2 + 15^2 = 1296 + 225 = 1521.

So it is a right triangle.

step-by-step explanation:

56.6

step-by-step explanation:

the ratio of the perimeters is equal to the scale.

the ratio of the areas is equal to the square of the scale.

34 / 20 = k

a / 19.6 = k²

substituting:

a / 19.6 = (34 / 20)²

a = 19.6 (34 / 20)²

a ≈ 56.6