ANSWER
AB=76 BC=357 AC=365 This triangle is a right triangle.
EXPLANATION
We use the Pythagoras Theorem to determine whether the triangles are right triangles.
According to this theorem, the square of the hypotebuse is equal to the sum of the squares of the two shorter legs.
We have:
AB=76 BC=357 AC=365
133225=5776+127449
133225=133225
For the second triangle, we have;
B) Triangle ABC: AB=123 BC=836 AC=845
845²=123²+826²
714025=15129+682276
714025≠697405
The first triangle is a right triangle