12 multiple-choice questions, progressively harder.
In the numbered diagram, ℓ∥m\ell\parallel mℓ∥m, m∠2=(5x+7)∘m\angle2=(5x+7)^\circm∠2=(5x+7)∘, and m∠6=(8x−20)∘m\angle6=(8x-20)^\circm∠6=(8x−20)∘. Find xxx.
Solution
Correct answer: B
Angles 2 and 6 are corresponding, so set their measures equal.
5x+7=8x−205x+7=8x-205x+7=8x−20
Subtract 5x5x5x and add 202020, giving 27=3x27=3x27=3x. Thus x=9x=9x=9. Each measure is then 52 degrees.
In the numbered diagram, ℓ∥m\ell\parallel mℓ∥m, m∠4=(3x+14)∘m\angle4=(3x+14)^\circm∠4=(3x+14)∘, and m∠5=(5x+22)∘m\angle5=(5x+22)^\circm∠5=(5x+22)∘. Find xxx.
Correct answer: D
Angles 4 and 5 are same-side interior angles, so add their measures.
3x+14+5x+22=1803x+14+5x+22=1803x+14+5x+22=180
Combining terms gives 8x+36=1808x+36=1808x+36=180, hence 8x=1448x=1448x=144 and x=18x=18x=18. The measures are 68 and 112 degrees, which total 180 degrees.
In the numbered diagram, ℓ∥m\ell\parallel mℓ∥m, m∠1=(7x−8)∘m\angle1=(7x-8)^\circm∠1=(7x−8)∘, and m∠7=(4x+28)∘m\angle7=(4x+28)^\circm∠7=(4x+28)∘. Find xxx.
Correct answer: A
Angles 1 and 7 are alternate exterior angles of parallel lines, so they are congruent.
7x−8=4x+287x-8=4x+287x−8=4x+28
Subtract 4x4x4x and add 888 to get 3x=363x=363x=36, hence x=12x=12x=12. Both expressions give 76 degrees.
In the numbered diagram, ℓ∥m\ell\parallel mℓ∥m, m∠2=(4x+11)∘m\angle2=(4x+11)^\circm∠2=(4x+11)∘, and m∠7=(6x+9)∘m\angle7=(6x+9)^\circm∠7=(6x+9)∘. Find xxx.
Correct answer: C
Angles 2 and 7 are same-side exterior angles, so their measures total 180 degrees.
4x+11+6x+9=1804x+11+6x+9=1804x+11+6x+9=180
This gives 10x+20=18010x+20=18010x+20=180 and then x=16x=16x=16. The measures 75 and 105 degrees pass the required sum check.
In the numbered diagram, ℓ∥m\ell\parallel mℓ∥m and m∠7=121∘m\angle7=121^\circm∠7=121∘. Find m∠4m\angle4m∠4.
Corresponding angles 3 and 7 are congruent, so angle 3 measures 121 degrees. Angles 3 and 4 form a linear pair.
m∠4=180∘−121∘=59∘m\angle4=180^\circ-121^\circ=59^\circm∠4=180∘−121∘=59∘
For the numbered crossings, let L=m∠4+m∠5L=m\angle4+m\angle5L=m∠4+m∠5 and R=m∠3+m∠6R=m\angle3+m\angle6R=m∠3+m∠6. Before imposing parallelism, angle addition gives L+R=360∘L+R=360^\circL+R=360∘. If L=191∘L=191^\circL=191∘, what is RRR?
The two interior sums together make two straight angles, even without parallelism.
R=360∘−191∘=169∘R=360^\circ-191^\circ=169^\circR=360∘−191∘=169∘
Since this is below 180 degrees, the angle postulate would force a meeting on the RRR side; this cannot be a parallel-line case.
For the numbered diagram with ℓ∥m\ell\parallel mℓ∥m, the proof has m∠1+m∠4=180∘m\angle1+m\angle4=180^\circm∠1+m∠4=180∘ and m∠4+m∠5=180∘m\angle4+m\angle5=180^\circm∠4+m∠5=180∘. Which step establishes ∠1≅∠5\angle1\cong\angle5∠1≅∠5?
Both sums equal 180 degrees, so their other terms are equal after subtracting the shared measure.
m∠1=m∠5m\angle1=m\angle5m∠1=m∠5
Equal measures mean the two angles are congruent. This derives corresponding congruence from the proved interior sum.
The three-line diagram gives ℓ∥m\ell\parallel mℓ∥m and m∥nm\parallel nm∥n. If m∠A=57∘m\angle A=57^\circm∠A=57∘, find m∠Cm\angle Cm∠C.
Carry the northeast angle AAA to the middle northeast angle by corresponding congruence for ℓ\ellℓ and mmm. Carry it again to the lower northeast angle using mmm and nnn. That lower angle measures 57 degrees.
The lower northeast and southeast angles form a linear pair.
m∠C=180∘−57∘=123∘m\angle C=180^\circ-57^\circ=123^\circm∠C=180∘−57∘=123∘
Two distinct transversals ttt and uuu each cross parallel lines ℓ\ellℓ and mmm. A selected angle made by ttt at ℓ\ellℓ measures 46∘46^\circ46∘; a selected angle made by uuu at ℓ\ellℓ measures 81∘81^\circ81∘. At mmm, select the angle corresponding to each of those two angles. What is the difference between the selected measures at mmm?
Corresponding congruence carries 46 degrees along ttt and 81 degrees along uuu. It does not identify an angle made by ttt with one made by uuu.
81∘−46∘=35∘81^\circ-46^\circ=35^\circ81∘−46∘=35∘
A transversal crosses two distinct coplanar lines, with no parallel condition given. Angles AAA and BBB are alternate interior angles. Which conclusion follows from that description alone?
The family name records position: both angles are between the crossed lines and on opposite sides of the transversal.
Congruence would follow from a parallel hypothesis, which has not been supplied. Neither a sum nor a shared vertex is part of this family definition.
In the numbered diagram with ℓ∥m\ell\parallel mℓ∥m, which two proved relationships establish ∠2≅∠8\angle2\cong\angle8∠2≅∠8?
Corresponding congruence gives ∠2≅∠6\angle2\cong\angle6∠2≅∠6. At the lower crossing, angles 6 and 8 are vertical and therefore congruent.
Transitivity gives ∠2≅∠8\angle2\cong\angle8∠2≅∠8, establishing this alternate exterior pair.
What is the correct order of dependence when deriving corresponding-angle congruence in this lesson?
The accepted angle postulate excludes either same-side interior sum being below 180 degrees for parallel lines. Their combined 360-degree total forces each sum to be 180 degrees.
Those sums and a local linear pair make corresponding angles supplements of the same angle. Congruent-supplements reasoning then gives their congruence.
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