Explore the conditions of the first kind of parallel lines (1)

1.4 ∠ 1 and ∠2, ∠3 and ∠4, ∠5 and ∠6, ∠7 and ∠8.

2. 120

3. Isometric angle of 3.FG and EC

4. It is known that the equivalent substitution angles are equal and two straight lines are parallel.

5.∫≈ 1 = 127 ,∴∠efb= 180- 127 = 53 .

∵∠ 2 = 53, ∴ab ∴∠efb=∠2 is parallel to the CD.

6.70

7.( 1)EF is parallel to BD.

≈aed = 60 ,∠ 1=∠2,∴∠ 1=∠2=30 .

∫∠3 = 30, ∴ef ∴∠ 1=∠3 is parallel to BD.

8.C

9.∠FCD=∠BAC

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