The completed two-column proof:
Statement Reason
∠ELG = 124° Given
∠FLG = 180° - ∠ELG = 56° Angle subtraction
∠FLG = ∠DLG Vertical angles
∠DLG = 2x° Given
2x° = 56° Transitive property of equality
x = 28° Solve for x
Therefore, x = 28°.
Linear pair: Angles that form a straight line are called linear pairs. The sum of the angles in a linear pair is 180 degrees.
Alternate interior angles: Alternate interior angles are pairs of non-adjacent angles on the inside of two parallel lines that are crossed by a transversal. Alternate interior angles are congruent.
Substitute: This means that we are replacing a term with an equivalent expression.
Subtract: This means that we are removing a term from both sides of an equation.
Divide both sides by 2: This means that we are dividing each term in the equation by 2.
Therefore, we have proven that x = 28.