二次方程,,唔明.

a)e^x-e^-x=5(e^x) e^x-e^-x = 5 e^x(e^x)^2 - 1 = 5e^x(e^x)^2 - 5e^x - 1 = 0e^x = 5.1925824 or -0.1925824(rejected)x = In 5.1925824 x = 1.64723...b)e^x+e^-x=3(e^x)^2 + 1 = 3e^x(e^x)^2 - 3e^x + 1 = 0e^x = 2.618034 or 0.381966x = In 2.618034 = 0.96242...or = In 0.381966 = -0.96242...

2010-09-24 21:47:53 補充：
a) 2nd line :

(e^x) (e^x-e^-x) = 5 e^x

2010-09-24 23:00:48 補充：
唔明 what ?

當e^x 是未知數 , 兩邊乘e^x,可變成 (e^x) 的二次方程,計到e^x , 再用In計x。

OK?