已知sin(π/2+a)=-3/5 且 π/2

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已知sin(π/2+a)=-3/5且π/2已知sin(π/2+a)=-3/5且π/2已知sin(π/2+a)=-3/5且π/2sin(π/2+a)=cos[π/2-(π/2+a)]=cos(-a)=c

已知sin(π/2+a)=-3/5 且 π/2
已知sin(π/2+a)=-3/5 且 π/2<=a<=π 则cos(π+a)

已知sin(π/2+a)=-3/5 且 π/2
sin(π/2+a)= cos[π/2-(π/2+a)] = cos(-a) = cosa = -3/5
cos(π+a)= -cosa =-(-3/5) =3/5