若cos(π/4+x)=3/5 17π/12

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若cos(π/4+x)=3/517π/12若cos(π/4+x)=3/517π/12若cos(π/4+x)=3/517π/12解析:若cos(π/4+x)=3/5,那么:sin2x=-cos(π/2+

若cos(π/4+x)=3/5 17π/12
若cos(π/4+x)=3/5 17π/12

若cos(π/4+x)=3/5 17π/12
解析:
若cos(π/4+x)=3/5,那么:
sin2x=-cos(π/2 +2x)
=-[2cos²(π/4+x) -1]
=-2cos²(π/4+x) +1
=-18/25 +1
=7/25

7/25