Answer:
A, C, D are true
Step-by-step explanation:
The Law of Cosines tells you that D is true. The equation of D is a rearrangement of the usual presentation of the Law of Cosines.
The given relationship between the squares of the side lengths tells you that C is true. (The relation would be "equals" if the triangle were a right triangle.)
D being true, together with the given condition, tells you that 2ab·cos(θ) must be less than zero. Since the side lengths are positive, the cosine must be less than zero, making statement A true. (When A is true, B cannot be true.)
