Sum of the three angles of a parallelogram = 280 degrees, find all the angles.

1. Vertices of the parallelogram – А, В, С, D. ∠А + ∠В + ∠С = 280 °.

2. To solve the problem, we will use two properties of the parallelogram:

– the total value of the angles on one side (adjacent) is 180 °, then

there is ∠А + ∠В = 180 °. ∠В = 180 ° – ∠А.

– the angles opposite each other are equal: ∠А = ∠С.

3. Substitute in the original expression (180 ° – ∠А) instead of ∠В and ∠А instead of ∠С:

∠А + 180 ° – ∠А + ∠А = 280 °.

∠А = 280 ° – 180 ° = 100 °.

∠В = 180 ° – 100 ° = 80 °

Answer: ∠А = ∠С = 100 °, ∠В = ∠D = 80 °.