1-5BBACD 6- 10CBDDA

1 1，II 12，BN 13，(-3， 1) 14，5 15， 180 16，80。

18,3619, π 20,2 cm or 8cm.

2 1, point a' (4,0), point B' (1 3), point c' (6,4).

22, the definition of vertical, AD‖EF,

The same angle is equal, two straight lines are parallel,

The two straight lines are parallel and the internal dislocation angles are equal.

Two lines are parallel, and the same angle is equal. If it is known, it will be equal.

23. solution: ∫a‖b,

∴∠ 2+∠ 1 = 180 (two straight lines are parallel with equal internal angles).

∴∠2= 180 -∠ 1= 180 - 105 =75

And \c‖d,

∴∠ 3 =∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠∠

24. Solution: Let this polygon have n sides.

(n-2)× 180=360×3- 180

The solution is n=7.

The number of sides of this polygon is 7.

25. Solution: Let the three external angles of this triangle be 2x, 3x and 4x respectively.

2x+3x+4x = 360°

The solution is x=40.

∴ 180-2x= 100, 180-3x=60, 180-4x=20

A: The degrees of the corresponding three internal angles are 100, 60 and 20 respectively.

26. solution: ∫In△ABC, ∠ B = 67, ∠ ACB = 74,

∴∠a= 180-∠b-∠ACB = 180-67-74 = 39

∠∠BDF is the outer corner of △ADE,

∴∠BDF=∠A+∠AED=39 +48 =87

27. Solution: ①∫ad is the height of △ABC, ∴ ∠ ADC = 90.

∴ In △ACD，∠DAC = 180-∠c-∠ADC = 180-70-90 = 20、

② In △ABC, ∠ BAC = 50, ∠ C = 70,

∴∠ABC= 180 -50 -70 =60

And ∵BF ∠ABC,

∴∠ABO=？ ∠ABC=？ ×60 =30 ,

The same ∠BAO=? ∠BAC=？ ×50 =25 ,

△ ∴, ∠ boa =180-∠ ABO-∠ Bao =180-30-25 =125 in △AOB.

28、( 1) 14、 17、20

(2)3n+2

(3) Solution: When n=35, 3n+2=3×35+2= 107.

Therefore, the perimeter of the figure consisting of 35 such trapeziums is 107.