若0°≤α≤90° ,sin六次方α+cos六次方α=1/4,则α等于多少
人气:226 ℃ 时间:2019-08-22 15:10:09
解答
sin六次方α+cos六次方α
=(sin²α)^3+(cos²α)^3
=(sin²α+cos²α)(sin^4 α-sin²α cos²α+cos^4 α)
=(sin² α)²-(sin² α)*(1-sin²α)+(1-sin²α)²
令sin²α=x
则x²-x*(1-x)+(1-x)²=¼
整理得,x²-x+¼=0
解得x1=x2=½
∴sin²α=½ ∴sinα=(√2)/2
∵α∈【0,π/2】,∴α=45°
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