Suppose a triangle has sides a, b, and c, and that a2 + b2 < c2. Let be the measure of the angle opposite the side of length c. Which of the following must be true? Check all that apply.
A. the triangle is not a right triangle.
B. a^2+b^2-c^2=2abcos(theta)
C. cos(theta) > 0
D. cos(theta) < 0