Question

八年级数学寒假作业课标版答案

Answer 1

证明：sinA+sinB+sinC
=2sin[(A+B)/2]cos[(A-B)/2]+sinC
=2cos(C/2)cos[(A-B)/2]+2sin(C/2)cos(C/2)
=2cos(C/2){cos[(A-B)/2]+cos[(A+B)/2]}
=2cos(C/2)[2cos(A/2)cos(B/2)]
=4（cosA/2）（cosB/2)(cosC/2)
根据和差化积，
sinA+sinB+sinC
=2sin[(A+B)/2]cos[(A-B)/2]+sinC
=2cos(C/2)cos[(A-B)/2]+2sin(C/2)cos(C/2)
=2cos(C/2){cos[(A-B)/2]+cos[(A+B)/2]}
=2cos(C/2)[2cos(A/2)cos(B/2)]
=4（cosA/2）（cosB/2)(cosC/2)

Answer 2

要么认真做 要么别做

追答

老师不看的 全凭自觉 抄不如不做 还浪费时间