作业帮cos^2(80)+sin^2(50)-sin190cos320=
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cos^2(80)+sin^2(50)-sin190cos320=
cos^2(80)+sin^2(50)-sin190cos320=
cos^2(80)+sin^2(50)-sin190cos320=
cos^2(80)+sin^2(50)-sin190cos320
=cos^2(80)+cos^2(40)+cos80cos40
=(cos80+cos40)^2-cos80cos40
=(2cos60cos20)^2-0.5(cos60+cos20)
=cos^2(20)-1/4-0.5cos20
=[cos20-1/4]^2-3/16
=[cos20-(1+√3)/4][cos20+(√3-1)/4]