tanπ/8+cosπ/8求值

求值，过程哈

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tanπ/4=1=2tanπ/8/(1-tan²π/8)
令tanπ/8=a
2a/(1-a²)=1
a²+2a-1=0
a=tanπ/8>0
所以a=-1+√肢答2

cosπ/4=√2/2=2cos²π/8-1
cos²π/8=(√2+2)/4
cosπ/8=√(√2+2)/历仿慧2
所以原式=-1+√大渣2+√(√2+2)/2

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