1、3 cm
2、8
3、30°,105°
4 - 6 B C A
7、由(b - 2)² + ∣c - 3∣ = 0得b = 2,c = 3.
又∵∣x - 4∣ = 2,
∴ x = 6或2,即a = 6或2.
当a = 6,b + c < 6不合题意,
当a = 2时,三角形的周长为7,此时三角形为等腰三角形.
8、设腰长为x cm,底为y cm.
答:各边长的长分别为10 cm,10 cm,12 cm.
9、(1)由BE、CF分别为AC、AB边的中线可得
AB = 6,AC = 4,
∴ BC = 18 - 6 - 4 = 8.
∵ 三角形的三条中线交于一点,
∴ D为BC的中点,
∴ BD = CD = 4.
(2)∵ F点是AB的中点,
∴ S△AOF = S△BOF
同理S△AOE = S△COE,S△BOD = S△COD
又S△ABD = S△ACD
∴ S△AOF + S△BOF + S△BOD = S△AOE + S△COE + S△OCD
∴ S△AFO = S△AOE.
同理可得:S△AOF= S△BOF = S△BOD = S△COD = S△COE = S△AOE
∴ S△BOD = 1/6S△ABC = 6 cm²
10、(1)30
(2)12
(3)S△ABC = 2S△ACD