积化和差公式:cosαsinβ=[sin(α+β)-sin(α-β)]/2
所以,cosAcosB=[sin(A+B)-sin(A-B)]/2
C=60°,则:A+B=120°
得:B=120°-A
所以,
cosAcosB=[sin120°-sin(2A-120°)]/2
=(-1/2)sin(2A-120°)+√3/4
易得:0°
积化和差公式:cosαsinβ=[sin(α+β)-sin(α-β)]/2
所以,cosAcosB=[sin(A+B)-sin(A-B)]/2
C=60°,则:A+B=120°
得:B=120°-A
所以,
cosAcosB=[sin120°-sin(2A-120°)]/2
=(-1/2)sin(2A-120°)+√3/4
易得:0°