Each a atom is adjacent to 3 b atoms. what is the a-c-b bond angle?

Using the simulation to build a system with 5 bonds. The resulting structure is called the Trigonal bipyramidal structure. The two different sites in a trigonal bipyramid are labeled as A and B in the drawing to the right. 
In this case, therefore, the bond angle A-C-B is 90 Degrees (right angle)

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