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In the cosine rule, a² − 2ab cos γ + b² − c² = 0 is a quadratic in a. How many positive roots can it have?
AOnly 1
BOnly 2
C0, 1 or 2
DExactly 3
Answer & Solution
Correct answer: C. 0, 1 or 2
Depending on the data, the quadratic can give two, one or no positive solutions, matching the possible triangles.
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