tan8分之派等于多少?怎么化呀
问题描述：
tan8分之派等于多少?怎么化呀
答
设x = π/8,
则2x = π/4,
tan2x = 2tanx/(1-(tanx)^2)
1 = 2tanπ/8 / (1- (tanπ/8)^2 )
1- (tanπ/8)^2 = 2 tanπ/8
(tanπ/8)^2 + 2tanπ/8 -1 =0
tanπ/8 = -1 +√2 或 tanπ/8 = -1+√2 ( 舍去)
∴tanπ/8 = -1 +√2