Answer
To find the sum of interior angles of a polygon help notes:
The formula for calculating the sum of interior angles of a polygon is ( n − 2 ) × 180 ∘ where “n” is the number of sides.
So for a triangle with 3 sides
( 3 - 2) x 180 = 180 degree angle sum.
4 sides polygon
( 4 - 2) x 180 = 360 degree angle sum
*If you have known angles except one, subtract them from the angle sum for that polygon to find the unknown angle.
*If you have each angle with an expression, put them all together in an equation = to angle sum of that polygon and solve.