作业帮8sin(45+a)sin(45-a)=1,sin^4a-cos^4a=
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8sin(45+a)sin(45-a)=1,sin^4a-cos^4a=
8sin(45+a)sin(45-a)=1,sin^4a-cos^4a=
8sin(45+a)sin(45-a)=1,sin^4a-cos^4a=
8sin(45+a)sin(45-a)=1
8sin(45+a)cos[90-(45-a)]=1
8sin(45+a)cos(45+a)=1
4sin[2(45+a)]=1
4sin(90+2a)=1
4cos2a=1
cos2a=1/4
原式=-(cos²a+sin²a)(cos²a-sin²a)
=-1×cos2a
=-1/4
8sin(45+a)sin(45-a)=8sin(45+a)cos(90-45+a)=8sin(45+a)cos(45+a)=4sin(90+2a)=4cos(90-90-2a)=4cos2a=1;
sin^4a-cos^4a=(sin^2a-cos^2a)（sin^2a+cos^2a）=sin^2a-cos^2a=（1-cos2a）/2 - (1+cos2a)/2=-1/4
8sin(45+a)sin(45-a)=1,sin^4a-cos^4a=
sin(45度+a)=
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