超簡單三角常識(急)!!!要求詳解

(1/2) ab sin (π/3) = √3
(1/2) ab √3/2 = √3
ab = 4 .....(1)a² + b² - c² - 2ab cos (π/3) = 0
a² + b² - 2² - 2ab (1/2) = 0
a² + b² - ab = 4 .....(2)(2) + 3*(1) :a² + b² + 2ab = 4 + 12
(a + b)² = 16
a + b = 4 .....(3)(2) - (1) :a² + b² - 2ab = 4 - 4
(a - b)² = 0
a - b = 0
a = b , 代入(3) :a = b = 2

2010-12-23 17:41:49 補充：
若三角形已知2邊a , b 及a , b夾角@ ,

則三角形面積 = (1/2) a b sin@