Answer:
B, C
Step-by-step explanation:
Let's go through each one to see which is valid
A: Isosceles triangles must have at least 2 sides of the same length. In this case all 3 sides are different. Hence A is NOT valid.
B. Obtuse triangles have one angle which is greater than 90 degrees. In this case, we have one angle greater than 90 degrees (i.e 120 deg). Hence B is valid.
C. Scalene triangles have sides whose lengths are all different. We see this evident in our triangle here. So C is valid.
D. Right triangles must have one angle exactly equal to 90 degree. We do not see this here. So D is NOT valid.
E. Equilateral triangles have 3 sides exactly the same length.We do not see this here. So E is NOT valid.
F.Acute triangles have all angles less than 90 degrees. Here we obviousy have one that is greater than 90 degrees (i.e 120 degrees) hence F is NOT Valid.
