(高一数学)答案看不懂,麻烦写下来拍下来,详细点。
2个回答
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sin(5π/4+α)=sin[π+(π/4+α)]= - sin(π/4+α)= -cos[(π/2)-(π/4+α)]
= - cos[(π/4)-α]
0<α<π/2
-(π/2)<-α<0
(π/4)-(π/2)<(π/4)-α<0+(π/4)
-(π/4<(π/4)-α<π/4
cos[(π/4)-α]>0
cos[(π/4)-α]=√(1-sin^2[(π/4)-α])=√(1-a^2)
所以,
sin(5π/4+α)=-√(1-a^2)
= - cos[(π/4)-α]
0<α<π/2
-(π/2)<-α<0
(π/4)-(π/2)<(π/4)-α<0+(π/4)
-(π/4<(π/4)-α<π/4
cos[(π/4)-α]>0
cos[(π/4)-α]=√(1-sin^2[(π/4)-α])=√(1-a^2)
所以,
sin(5π/4+α)=-√(1-a^2)
追问
我说的是写下来拍下来
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