Question in-con
In convex pentagon , segment is parallel to segment . The measure of angle is degrees, and the measure of angle is degrees. What is the measure, in degrees, of angle ?
In convex pentagon A B C D E , segment A B is parallel to segment
Hard-difficulty · SAT Math · Lines, Angles, and Triangles — Angle relationships (parallel lines). Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.
Answer explanation
The correct answer is . It's given that the measure of angle is degrees. Therefore, the exterior angle formed by extending segment at point has measure , or , degrees. It's given that segment is parallel to segment . Extending segment at point and extending segment at point until the two segments intersect results in a transversal that intersects two parallel line segments. One of these intersection points is point , and let the other intersection point be point . Since segment is parallel to segment , alternate interior angles are congruent. Angle and the exterior angle formed by extending segment at point are alternate interior angles. Therefore, the measure of angle is degrees. It's given that the measure of angle in pentagon is degrees. Therefore, angle has measure , or , degrees. Since angle in pentagon is an exterior angle of triangle , it follows that the measure of angle is the sum of the measures of angles and . Therefore, the measure, in degrees, of angle is , or .
Alternate approach: A line can be created that's perpendicular to segments and and passes through point . Extending segments and at points and , respectively, until they intersect this line yields two right triangles. Let these intersection points be point and point , and the two right triangles be triangle and triangle . It's given that the measure of angle is degrees. Therefore, angle has measure , or , degrees. Since the measure of angle is degrees and the measure of angle is degrees, it follows that the measure of angle is , or , degrees. It's given that the measure of angle is degrees. Therefore, angle has measure , or , degrees. Since the measure of angle is degrees and the measure of angle is degrees, it follows that the measure of angle is , or , degrees. Since angles , , and angle in pentagon form segment , it follows that the sum of the measures of those angles is degrees. Therefore, the measure, in degrees, of angle is , or .
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