2R=sinA/a=sinB/b=sinC/c
2(sinB)^2=(sinA)^2+(sinC)^2
4R(sinB)^2=2R(sinA)^2+2R(sinC)^2
2bb=aa+cc
2bb=2(aa+cc-bb)
bb=bb
2bb=2bb
(aa+bb-cc)+(bb+cc-aa)=2(aa+cc-bb)
(aa+bb-cc)R/(2abc)+(bb+cc-aa)R/(2abc)=2(aa+cc-bb)R/(2abc)
(aa+bb-cc)/(2absinC)+(bb+cc-aa)/(2bcsinA)=2(aa+cc-bb)/(2acsinB)
cosC/sinC+cosA/sinA=2cosB/sinB
cotC+cotA=2cotB
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由 bugzpodder 於 星期六 八月 30, 2003 9:19 am
[問題]證明
由 heron0520 於 星期四 七月 24, 2003 5:54 pm
ABC is any triangle
if 2(sinB)^2=(sinA)^2+(sinC)^2
prove that 2cotB=cotA+cotC
if 2(sinB)^2=(sinA)^2+(sinC)^2
prove that 2cotB=cotA+cotC