hiyoung
幼苗
共回答了25个问题采纳率:88% 举报
1.∵A=π-(B+C),sinA=cosBcosC
∴sin(B+C)=cosBcosC,
即sinBcosC+cosBsinC=cosBcosC.
∴tanB+tanC
=sinB/cosB+sinC/cosC
=(sinBcosC+sinCcosB)/(cosBcosC)
=(cosBcosC)/(cosBcosC)
=1.
2.令tanx=-1
∴x=kπ-π/4或x=kπ+3π/4
∴sin2x=sin(2kπ-π/2)=-1
或sin2x=sin(2kπ+3π/2)=-1
即:f(-1)=-1
1年前
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