In triangle ABC, angle 2 = 60 degrees, angle 3 = 70 degrees, find angle 1.

The sum theorem of the angles of a triangle says that the sum of all three angles of any triangle is 180 degrees, so you can write the expression:
angle 1 + angle 2 + angle 3 = 180 degrees.
Substitute the known values into the resulting expression:
angle 1 + 60 degrees + 70 degrees = 180 degrees;
angle 1 = 180 degrees – 60 degrees – 70 degrees;
angle 1 = 50 degrees.
Answer: 50 degrees.