Answer:
1. Statement: m∠AOB = 180°
1. Reason: Straight Angle
2. Statement: m∠AOF + m∠FOG + m∠GOB = m∠AOB
2. Reason: Angle Addition Postulate
3. Statement: 5x - 15° + 90° + 2x = 180°
3. Reason: Substitution
4. Statement: x = 15°
4. Reason: Algebra
Explanation:
Part 1
Statement: m∠AOB = 180°
Reason: Straight Angle
Straight angle: An angle that is equal to 180°.
Part 2
Statement: m∠AOF + m∠FOG + m∠GOB = m∠AOB
Reason: Angle Addition Postulate
Angle Addition Postulate: When two or more angles are placed side by side such that they share a common vertex (and a common arm between each pair of angles), the sum of those angles will be equal to the total sum of the resulting angle.
Part 3
Statement: 5x - 15° + 90° + 2x = 180°
Reason: Substitution
Substitute the expression for each angle given in the diagram:
⇒ m∠AOF + m∠FOG + m∠GOB = m∠AOB
⇒ 5x - 15° + 90° + 2x = 180°
Part 4
Statement: x = 15°
Reason: Algebra
Solve the algebraic equation from part 3:
⇒ 5x - 15° + 90° + 2x = 180°
⇒ 5x + 2x + 90° - 15° = 180°
⇒ 7x + 75° = 180°
⇒ 7x + 75° - 75° = 180° - 75°
⇒ 7x = 105°
⇒ 7x ÷ 7 = 105° ÷ 7
⇒ x = 15°