Question

How do you know 37? I don't understand, do you add another line connecting it to make a whole triangle or ..I don't understand..

Answer 1

Hello,
The 3th angle of the triangle is the supplement of 3x-8:
180-(3x-8)=180-3x+8=188-3x

The sum of all angles of the triangle is 180
180=2x+21+188-3x
==>180=-x+21+188
==>x=21+188-180
==>x=21+8
==>x=29