1 - 4 C C D B
5 - 7 C D D
8、2 cm
9、9.6 cm,9.6 cm,4.8 cm
10、7
11、75°
12、75°
13、80°或100°
14、9 cm
15、设BC = x,则AC = 2x.AB = 2x - 2.
依题意:2x + 2x - 2 + x = 18,
∴ 5x = 20,x = 4,
三角形的三边长分别为BC = 4 cm,AC = 8 cm,AB = 6cm.
16.如图11 - 11.
∵ ∠ACD = ∠B + ∠BAC,
∴ ∠BAC = 70° - 30° = 40°,
∵ AE平分∠BAE,
∴ ∠1 = ∠2 = 20°,
∴ ∠AED = ∠B + ∠2 = 50°.
17、∠ACB = 90°
18、(1)∵ ∠B = 35°,∠ACB = 85°,
∴ ∠BAC = 60°,
∵ AD平分∠BAC,
∴ ∠BAD = 30°,
∴ ∠ADE = 35° + 30° = 65°,
∵ ∠DPE = 90°
∴ ∠:E = 25°.
(2)∠E = 1/2(∠ACB - ∠B)或∠E = 1/2(∠B - ∠ACB).
19.(1)150° 90°
(2)不变化.
由(1)知∠ABC + ∠ACB = 150°,
∠XBC + ∠XCB = 90°,
∴ ∠ABX + ∠XCA = 150° - 90° = 60°.