Atriangle has side lengths 10, 15, and 7. is the triangle acute, obtuse, or right? show your work and explain.

The triangle cannot be a right angled triangle as it does not abide by Pythagoras' theorem, a²+b²=c² 
Because c² would need to be a smaller value for it to be right angle, the angle must be greater than 90, and therefore obtuse.