已知函数f(x)=Asin(3x +φ),(A>0,x∈(-∞,+∞),0

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已知函数f(x)=Asin(3x +φ),(A>0,x∈(-∞,+∞),0
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已知函数f(x)=Asin(3x +φ),(A>0,x∈(-∞,+∞),0
已知函数f(x)=Asin(3x +φ),(A>0,x∈(-∞,+∞),0

已知函数f(x)=Asin(3x +φ),(A>0,x∈(-∞,+∞),0
(1)当x=π/12时,f(π/12)=Asin(π/4 +φ)=4
所以A=4,φ=π/4
f(x)的最小值为-4
(2)f(x)=4sin(3x +π/4)
(3)f(2a/3+π /12)
=4sin(2a+π/2)
=-4cos2a
=-4(1-2sin^a)
=12/5
解得sina=2/√5或sina=-2/√5