Question

15,36,39 is it pythagorean triplet

Answer 1

yes it is Pythagorean triplet

Answer 2

$let \: 15 = a \: 36 = b \: 39 = c \\ a {}^{2} = b + c \\ lhs = 15 {}^{2} \\ = 15 \times 15 = 225 \\ rhs = 36 + 39 \\ = 75 \\ so \: lhs \: is \: not \: equal \: to \: rhs \\ so \: it \: is \: not \: a \: pythagorean \: triplet$
$c - b = 2 \\ = 39 - 36 = 3$
so it is not