Answer:
No, it is not a right triangle.
Explanation:
The simplest way to determine is testing out the numbers with Pythagorian theorem.
If it complies with the theorem, it is a right triangle.
let's assume c = 28, b = 21, and a = 20
the longest side is the hypotenuse so side c (28 in) will be the hypotenuse.
According to the Pythagorian theorem, the square of the length of hypotenuse must equal to the sum of squares of other two sides.
check:
c^2 = 28^2 = 784
a^2 + b^2 = 21^2 + 20^2 = 841
because c^2 is not equal to a^2 + b^2, the triangle is not a right triangle.