只是有2222222222條啦

(i)AB=a+b
CA=a+c
(ii)BC=b+c
s=(AB+CA+BC)/2
=abc
Aera of ∆ABC :
√{[(a+b+c)[(a+b+c)-AB][(a+b+c)-BC][(a+b+c)-AC]}
=√[(a+b+c)(c)(a)(b)]
=√[(a+b+c)(abc)]

(iii)∵a=5,b=6 and c=4
∴Aera of ∆ABC=√[(a b c)(abc)]
=√[(5 6 4)(5x6x4)]
=√[(15)(120)]
=√1800
18.
∠ABD=180˚-60˚(adj. ∠s on st. line)
=120˚
∠ADB=180˚-30˚-120˚(∠sum of ∆)
=30˚
∵∠ADB=∠BAD
∴BD=6cm
DC=6sin60˚
=2√3cm