Question triang

4.1 Lines, Angles, and Triangles - Angle relationships (parallel lines)
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  • Triangle upper L upper M upper R has a common vertex with triangle upper P upper Q upper R.
  • The common vertex is upper R.
  • A note indies the figure is not drawn to scale.

 

In the figure, LQ¯ intersects MP¯ at point R , and LM¯ is parallel to PQ¯. The lengths of MR¯LR¯, and RP¯ are 6 , 7 , and 11 , respectively. What is the length of LQ¯?

A.

119 11

B.

77 6

C.

113 6

D.

119 6

Triangle upper L upper M upper R has a common vertex with triangle upper P upper

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

Choice D is correct. The figure shows that angle MRL and angle PRQ are vertical angles. Since vertical angles are congruent, angle MRL and angle PRQ are congruent. It’s given that LM¯ is parallel to PQ¯. The figure also shows that LQ¯ intersects LM¯ and PQ¯. If two parallel segments are intersected by a third segment, alternate interior angles are congruent. Thus, alternate interior angles MLR and PQR are congruent. Since triangles LMR and PQR have two pairs of congruent angles, the triangles are similar. Sides LR and MR in triangle LMR correspond to sides RQ and RP, respectively, in triangle PQR. Since the lengths of corresponding sides in similar triangles are proportional, it follows that RQLR=RPMR. It's given that the lengths of MR¯, LR¯, and RP¯ are 6 , 7 , and 11 , respectively. Substituting 6 for MR, 7 for LR, and 11 for RP in the equation RQLR=RPMR yields RQ7=116. Multiplying each side of this equation by 7 yields RQ=1167, or RQ=776. It's given that LQ¯ intersects MP¯ at point R , so LQ=LR+RQ. Substituting 7 for LR and 776 for RQ in this equation yields LQ=7+776, or LQ=1196. Therefore, the length of LQ¯ is 1196.

Choice A is incorrect and may result from conceptual or calculation errors.

Choice B is incorrect. This is the length of RQ¯, not LQ¯.

Choice C is incorrect and may result from conceptual or calculation errors.