貼現率 (discount rate) - 財經

請問各位大大
貼現率是不是有很多種算法?
我查了一下書
發現有許多種算法
可是不確定他們是不是一樣的

1. 假設某公司的after tax cost of debt is 6％
an estimated cost of equity of 16%
and future gearing comprising 20% debt and 80% equity
那麼貼現率的算法為
---------------------------------------
Weight Cost Weighted cost
A B A x B %
% % %
Debt 20 6 1.2
Equity 80 16 12.8
---------------------------------------
Discount Rate 14%
(Source:Mills and Robertson, Fundatmentals of Managerial Acoounting and Finance)

2. WACC (weighted average cost of capital)

debt/Total Financing (Cost of debt)(1-Tax)
+ equity/Total Financeing (cost of equity)
------------------------------------------
WACC

Example
The market value of debt = $300 million
The market value of equity = $400 million
The cost of debt = 8%
The corporate tax rate = 35%
The ocst of equity is 18%

WACC = 12.5%
(Source: http://www.valuebasedmanagement.net/methods_wacc.html)

以上數字都為假設
只是想請問 這兩種算法 是一同一種嗎?
某公司用這兩種算法 會出來同樣的貼現率嗎?
看半天看不出各所以然來
在網路搜尋還搜尋到其他種算法(很明顯是跟這兩種有差異的)

所以想請大家幫忙指點一下
謝謝^^

--