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A pair of parallel lines is intersected by a transversal such that ∠1 and ∠2 form a pair of alternate interior angles. If m\angle 1 =75°, what is the measure of ∠2?
75°
105°
65°
15°
75°
For any pair of parallel lines cut by a transversal, all alternate interior angles are equal; therefore, if one is 75°, the other must also be 75°.
Two parallel lines intersected by a transversal. Angle 1 and Angle 2 are alternate interior angles. The measure of angle 1 is 75 degrees.
∠1=∠2
For any pair of parallel lines cut by a transversal, all alternate interior angles are equal; therefore, if one is 75°, the other must also be 75°.
Confusing alternate interior angles with consecutive interior angles (which sum to 180°) or vertically opposite angles.
Identify Relationship
The problem states that ∠1 and ∠2 are alternate interior angles formed by a transversal intersecting two parallel lines.
∠1=∠2
Apply Geometric Property
According to the Alternate Interior Angles Theorem, when two parallel lines are cut by a transversal, the alternate interior angles are equal in measure.
m∠1=m∠2
Calculate Measure
Given m∠1=75°, we substitute this into the equality equation to find m∠2.
m∠2=75°
A is correct because when a transversal intersects two parallel lines, the alternate interior angles are always equal, so the measure of angle 2 is 75°.
This concept is foundational for solving problems involving polygon angle sums and coordinate geometry slopes where lines are parallel.