期中测试1.80°2.103.(1)8(2)0.194.(4)5.20°6.60° 57.209.B10.A11.C12.D13.C14.C15.B16.C17.证明:∵四边形ABCD为平行四边形∴AB=CD, ∠B=∠D在△BAE和△DCF中,AB=CD,∠B=∠D,∠BAE=∠DCF∴△BAE≌△DCF∴AE=CF18.(1)(2)(3)当射击数很大时,击中的概率估值为0.8219.(1)20 32%(2)(3)900×(20+16+2)÷50=684(名)20.证明: ∵四边形ABCD式平行四边形,∴AD//BC,∠ABC=∠ADC∵BE、 DF分别平分∠ABC、 ∠ADC,∴∠ABE=∠CBE, ∠AEB=∠CBE, ∠CDF=∠ADF∴∠ABE=∠AEB,∠CFD=∠CDF,又∵∠ABC=∠ADC,∴∠AEB=∠ADF,∴BE //DF∵DE//BF, 则四边形DEBF为平行四边形又∵EF、BD为平行四边形对角线∴BD、EF互相平分21.(1)设∠BAE=x∴∠EAD=2∠BAE=2x,∠BAD=3x∵AB=AE,∠BAE=x∵AD//BC∴∠ABC+∠BAD=180°x=36°即∠BAE=36°(2)相等∵∠BAD=3∠BAE=108°∴∠ABC=180°-108°=72°∴∠ABD=∠BAE∴BF=AF22.解: (1) DE⊥AC证明∵BD=2AD, BD=2A |