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Printjmc
geometry junior
Problem
An equilateral triangle shares a common side with a square as pictured. What is the number of degrees in (not pictured)? 
Solution
First of all, for our benefit, we should draw in the desired angle: We can see that thus is an isosceles triangle, where Since the other two angles are equal and add up to , we have that Likewise,
Then,
Then,
Final answer
30^\circ.