Alpha, Beta and Gamma are inner angles in a triangle.

Alpha, Beta and Gamma are inner angles in a triangle. If Alpha = Beta + Gamma, what can't be the size of Beta?

Quiz

Answer/Solution

90 degrees.

Steps/Work

Given Alpha = Beta + Gamma, and Alpha, Beta and Gamma are inner angles in a triangle. Thus Alpha + Beta + Gamma = 180
Beta + Gamma + Beta + Gamma = 180 => 2(Beta + Gamma) = 180 => Beta + Gamma = 90. Thus beta will be less than 90.
Hence the answer is D.