如何化简成第二步.

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如何化简成第二步.如何化简成第二步. 如何化简成第二步.msin(x+Pai/4)sin(x-Pai/4)=m[sinxcosPai/4+cosxsinPai/4][sinxcosPai/4

如何化简成第二步.
如何化简成第二步.
 

如何化简成第二步.
msin(x+Pai/4)sin(x-Pai/4)
=m[sinxcosPai/4+cosxsinPai/4][sinxcosPai/4-cosxsinPai/4]
=m*根号2/2(cosx+sinx)*根号2/2(sinx-cosx)
=-m/2(cos^2x-sin^2x)
=-m/2cos2x

无望,忘记了

m*sin(x+π/4)*sin(x-π/4)
=m*cos(x-π/4)*sin(x-π/4)
=m/2*2sin(x-π/4)*cos(x-π/4)
=m/2*sin(2x-π/2)
=-m/2*cos(2x)

msin(x+π/4)sin(x-π/4)
=m/2[sin(x+π/4)sin(x-π/4)+sin(x+π/4)sin(x-π/4)]
=m/2[sin(x+π/4)sin(x-π/4)+cos(π/4-x)cos(x+π/4)]
=m/2[cos(x-π/4)cos(x+π/4)+sin(x+π/4)sin(x-π/4)]
=m/2*cos(x-π/4+x-π/4)
=m/2*cos2x