Question in-rig

4.1 Lines, Angles, and Triangles - Angle relationships (parallel lines)
0:00

In right triangle A B C , angle C is the right angle and B C = 162 . Point D on side A B is connected by a line segment with point E on side A C such that line segment D E is parallel to side B C and C E = 2 A E . What is the length of line segment D E ?

Enter your answer:

In right triangle A B C , angle C is the right angle and B C

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 54 . It’s given that in triangle A B C , point D on side A B is connected by a line segment with point E on side A C such that line segment D E is parallel to side B C . It follows that parallel segments D E and B C are intersected by sides A B and A C . If two parallel segments are intersected by a third segment, corresponding angles are congruent. Thus, corresponding angles C and AED are congruent and corresponding angles B and A D E are congruent. Since triangle A D E has two angles that are each congruent to an angle in triangle A B C , triangle A D E is similar to triangle A B C by the angle-angle similarity postulate, where side D E corresponds to side B C , and side A E corresponds to side A C . Since the lengths of corresponding sides in similar triangles are proportional, it follows that DEBC=AEAC. Since point E lies on side A C , A E + C E = A C . It's given that C E = 2 A E . Substituting 2 A E for C E in the equation A E + C E = A C yields AE+2AE=AC, or 3 A E = A C . It’s given that B C = 162 . Substituting 162 for B C and 3 A E for A C in the equation DEBC=AEAC yields DE162=AE3AE, or DE162=13. Multiplying both sides of this equation by 162 yields D E = 54 . Thus, the length of line segment D E is 54 .