Is 9,12,15 a right triangle?

Yes.

Step-by-step explanation:

Use the Pythagorean thereom to check. 9^2+12^2=15^2

225=225

So yes.

Yes, is a right triangle

Step-by-step explanation:

To know if you can build a right triangle with those sides we have to make the following equality

h² = l1² + l2²

The hypotenuse is always the longest side so it should be 15

we check the equality of the equation

15² = 9² + 12²

225 = 81 + 144

225 = 225

Equality was fulfilled so it is a right triangle