根号[1+cosa/1-cosa]+根号[1-cosa/1+cosa]……A.2/sinaB.-2/sinaC.2/|sina|D.-2/|cosa|
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![根号[1+cosa/1-cosa]+根号[1-cosa/1+cosa]……A.2/sinaB.-2/sinaC.2/|sina|D.-2/|cosa|](/uploads/image/z/14098210-34-0.jpg?t=%E6%A0%B9%E5%8F%B7%5B1%2Bcosa%2F1-cosa%5D%2B%E6%A0%B9%E5%8F%B7%5B1-cosa%2F1%2Bcosa%5D%E2%80%A6%E2%80%A6A.2%2FsinaB.-2%2FsinaC.2%2F%7Csina%7CD.-2%2F%7Ccosa%7C)
根号[1+cosa/1-cosa]+根号[1-cosa/1+cosa]……A.2/sinaB.-2/sinaC.2/|sina|D.-2/|cosa|
根号[1+cosa/1-cosa]+根号[1-cosa/1+cosa]
……
A.2/sina
B.-2/sina
C.2/|sina|
D.-2/|cosa|
根号[1+cosa/1-cosa]+根号[1-cosa/1+cosa]……A.2/sinaB.-2/sinaC.2/|sina|D.-2/|cosa|
√[(1+cosa)/(1-cosa)]+√[(1-cosa)/(1+cosa)]
=√[(1+cosa)²/(1-cosa)(1+cosa)]+√[(1-cosa)²/(1+cosa)(1-cosa)]
=√[(1+cosa)²/sin²a]+√[(1-cosa)²/ sin²a]
=(1+cosa)/∣sina∣+∣(1-cosa)/∣sina∣
=2/∣sina∣
故:选C
C
a