The Triangle Angle Sum Theorem states that the sum of the angles inside a triangle must equal 180°. Using this theorem, find the measure of angle B.
To find the measure of angle B, we can start by calculating the sum of the angles in triangle ABC:
angle A + angle B + angle C = 180°
Since we know the measure of angle A is 70° and angle C is 40°, we can substitute these values into the equation:
70° + angle B + 40° = 180°
Simplifying the equation, we get:
110° + angle B = 180°
Now, we can isolate angle B by subtracting 110° from both sides:
angle B = 180° - 110°
angle B = 70°
Therefore, the measure of angle B is 70°.