cos［arccsc(1241/280)］，要用几分之几的分数值表示

cos arc csc (1241/280)

=cos arc sin (280/1241)

=cos arc cos √[1-(280/1241)²]

=1209/1241

设 x = arccsc(1241/280)，则 cscx = 1241/280，

cosx = [ √( 1241^2 - 280^2 ) ]/1241= 1209/1241；

故 cos[ arccsc(1241/280) ] = cosx = 1209/1241 。