若sin(π/4+Q)=3/5(0

若sin(π/4+Q)=3/5(0
若sin(π/4+Q)=3/5(0

若sin(π/4+Q)=3/5(0
sin(π/4+Q)=3/5
0π/4<π/4+Q<π/2
∴cos(π/4+Q)=4/5
cos2Q
=sin(π/2+2Q)
=sin[2(π/4+Q)]
=2sin(π/4+Q)cos(π/4+Q)
=2×3/5×4/5
=24/25
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由sin(π/4+Q)=3/5 cos(π/4+Q)=4/5 (0

Q在四分之拍到二分之拍之间，无解。