为什么得出B,为什么-0.8？
问题如下图：
选项：
A. 
B. 
C. 
解释：
NO.PZ2018091705000024 Allen is investment manager, who recently recruitea new customer, Polly. Polly investe$100,000 in asset for 20 years thpromises to offer annucapitgain of 8%, whiare ferrecapitgains. The investment account is expecteto taxe15% when capitgains are realize Assume beginning of the investment perio the investment ha cost basis of $80,000, Calculate the post-tvalue of the investment after 20 years later. $411,181.36 $372,756.35 $ 408,181.36 C is correct. 考点ferreCapitGain T解析首先，我们计算一下B = 80,000/100,000=0.8 接着我们运用税基基础不等于1时候的ferreCapitGain Tax计算，即 lFV=PV[(1+R)N−[(1+R)N−B]×TCG]100,000[(1+8%)20−[(1+0.08)20−0.8]×15%]=408,181.36{l}FV=PV{\lbrack{{(1+R)}^N-\lbrack{(1+R)}^N-B\rbrack\times T_{CG}}\rbrack}\\100,000{\lbrack{(1+8\%)}^{20}-{\lbrack{(1+0.08)}^{20}-0.8\rbrack}\times15\%\rbrack}=408,181.36lFV=PV[(1+R)N−[(1+R)N−B]×TCG]100,000[(1+8%)20−[(1+0.08)20−0.8]×15%]=408,181.36 可否这样计算(1+8%)^20-[(1+8%)^20-1]*0.15-(1-0.8)*0.15 上面这个是blentaxing里稅基不是1的算法，为什么两个地方不一样？
Allen is investment manager, who recently recruitea new customer, Polly. Polly investe$100,000 in asset for 20 years thpromises to offer annucapitgain of 8%, whiare ferrecapitgains. The investment account is expecteto taxe15% when capitgains are realize Assume beginning of the investment perio the investment ha cost basis of $80,000, Calculate the post-tvalue of the investment after 20 years later. $411,181.36 $372,756.35 $ 408,181.36 C is correct. 考点ferreCapitGain T解析首先，我们计算一下B = 80,000/100,000=0.8 接着我们运用税基基础不等于1时候的ferreCapitGain Tax计算，即 lFV=PV[(1+R)N−[(1+R)N−B]×TCG]100,000[(1+8%)20−[(1+0.08)20−0.8]×15%]=408,181.36{l}FV=PV{\lbrack{{(1+R)}^N-\lbrack{(1+R)}^N-B\rbrack\times T_{CG}}\rbrack}\\100,000{\lbrack{(1+8\%)}^{20}-{\lbrack{(1+0.08)}^{20}-0.8\rbrack}\times15\%\rbrack}=408,181.36lFV=PV[(1+R)N−[(1+R)N−B]×TCG]100,000[(1+8%)20−[(1+0.08)20−0.8]×15%]=408,181.36 请问这里为什么不能用:(1+8%)*20✘(1-15%)-(1–80/100)✘15%呢？我这里有点混乱了，我这个做法错在哪里呢？
