已知锐角a,β满足cosa=3/5,cos(a+β)=-5/13,则cosβ=
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已知锐角a,β满足cosa=3/5,cos(a+β)=-5/13,则cosβ=
已知锐角a,β满足cosa=3/5,cos(a+β)=-5/13,则cosβ=
已知锐角a,β满足cosa=3/5,cos(a+β)=-5/13,则cosβ=
cosa=3/5,sina=4/5
cos(a+β)=-5/13,sin(a+β)=12/13
cosβ
=cos[(a+β)-a]
=cos(a+β)cosa+sin(a+β)sina
=-5/13*(3/5)+12/13*(4/5)
=33/65
a、β为锐角,cos(a β)