Suppose a triangle has sides a, b, and c, and that a² + b² < c². Let 9 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. cose < 0
C. cose > 0
□ D. a² + b²-c² = 2abcose
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