1、165°
2、100°,400°40°
3、a = β + γ
4、D 5、A
6、如图11 - 6.
∵ CD平分∠ACB,
∴ ∠1 = ∠2,
∵ ∠A = ∠1 + ∠2 = 2∠1.
∵ ∠DCE = 54°,
∴ ∠4 = 36°,
∴ ∠A + ∠1 = 36°,
即3∠1 = 36°,∠1 = 12°,
∴ ∠A = 2∠1 = 24°.
7、如图11 - 7.
∵ ∠1 = 90° - ∠A = 80°
∴ ∠2 = 80°
∴ ∠3 = 80° - 10° = 70°
∴ ∠4 = 70°
∴ ∠5 = ∠4 - ∠A = 60°
∴ ∠6 = 60°
∴ ∠F = ∠6 - ∠A = 50°
8、(1)∠P = 90 - 150°/2 = 90° - 75° = 15°;
(2)∠P = 90° - 1/2∠A;
(3)证明:∠DBC = ∠A + ∠BCA,∠BCE = ∠A + ∠ABC,
∴ ∠DBC + ∠BCE = ∠A + ∠BCA + ∠ABC + ∠A = 180° + ∠A,
∵ BP、PC分别是∠DBC和△ECB的平分线,
∴ ∠BCP = 1/2∠BCE,∠CBP = 1/2∠DBC,
∴ ∠BCP + ∠CBP = 1/2(180° + ∠A) = 90° + ∠A/2,
∴ ∠P = 180° - (90° + 1/2∠A) = 90°- 1/2∠A