Answer:
Step-by-step explanation:
The three angles of a triangle always have to equal 180 in the end, so if you use the method which is the 4 in this instance, it is an obtuse angle that is equal to the top and left angle. You can add 1 and 2 to get 4, and do 4-3 to get 1+2, So, 4=1+2.
