已知函数f(x)=2sin(1/3x-π/6)(1)求f(5π/4) (2)设α,β∈[0,π/2],f(3α+π/2)=10/13,f(3β+π/2)=6/5.求cos(α+β)的值.

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已知函数f(x)=2sin(1/3x-π/6)(1)求f(5π/4) (2)设α,β∈[0,π/2],f(3α+π/2)=10/13,f(3β+π/2)=6/5.求cos(α+β)的值.
已知函数f(x)=2sin(1/3x-π/6)
(1)求f(5π/4)
(2)设α,β∈[0,π/2],f(3α+π/2)=10/13,f(3β+π/2)=6/5.求cos(α+β)的值.

已知函数f(x)=2sin(1/3x-π/6)(1)求f(5π/4) (2)设α,β∈[0,π/2],f(3α+π/2)=10/13,f(3β+π/2)=6/5.求cos(α+β)的值.
(1)π=180°
所以f(5π/4) =2sin(5/4*1/3π-π/6)=2sin45°=根号2
(2)f(3α+π/2)=2sin(α+π/6-π/6)=2sinα=10/13 sinα=5/13
f(3β+π/2)=2sinβ=6/5 sinβ=3/5
因为sin^2(α)+cos^2(α)=1且α,β∈[0,π/2],
所以cosα=12/13 cosβ=4/5
cos(α+β)=cosαcosβ-sinαsinβ=33/65

(1)根号2
(2)33/65

1.代进去总会吧 这都不会还是别浪费时间了
2.33/65
楼主高几? 这都不会可不行啊