Answer:
The three interior angles of a triangle must equal 180 degrees. The base angles must be the same degree for a triangle to be isosceles. We can set x as the measure of one base angle, and write an equation.
40 + 2x = 180
Subtract 40 from both sides.
2x = 140
Divide both sides by 2.
x = 70
The measure of a base angle is 70 degrees.
:)
