5/ The side of a triangle are 4,5, and 6 is it a right triangle.

Yes
No***

6.The sides of a triangle are 15,16, and 25 is it a right triangle?

Yes***
No

Pythagorean Theorem

a^2 + b^2 = Hyp^2

16 + 25 ≠ 36

225 + 256 ≠ 625