Three squares are joined together as shown in figure to create a triangle.
What is the sum of angles ∠A+∠B+∠C ?
Note: We are referring to the "exterior angles", not the interior angles of the triangle.
Let the three interior angles of the triangle be A', B', and C'
Then, A = 360o - 90o - 90o - A' = 180o - A'.
B = 360o - 90o - 90o - B' = 180o - B'.
C = 360o - 90o - 90o - C' = 180o - C'.
A + B + C = ( 180o - A' ) + ( 180o - B' ) + ( 180o - C' ) = 540o - A' - B' - C' = 540o - ( A' + B' + C' )
= 540o - 180o = 360o