cos(α-55)cos(α+5)+sin(α-55)sin（α+5）
=(cosacos55+sinasin55)(cosacos5-sinasin5)+(sinacos55-cosasin55)(sinacos5+cosasin5)
=(cosacos55+sinasin55)(cosasin55-sinacos55)+(sinacos55-cosasin55)(sinasin55+cosacos55)
=(cosacos55+sinasin55)(cosasin55-sinacos55+sinacos55-cosasin55)
=(cosacos55+sinasin55)*0
=0