siuhochung 寫到:tanA/tanB=aa/bb
a/b=sinA/sinB
cosB/cosA=a/b
acosA=bcosB
a[(bb+cc-aa)/2bc] = b[(aa+cc-bb)/2ac]
aa(bb+cc-aa) = bb(aa+cc-bb)
aacc-aaaa=bbcc-bbbb
cc(aa-bb)=(aa-bb)(aa+bb)
aa-bb is not 0
so cc=aa+bb
是個直角三角形
有人很笨
tanA/tanB=aa/bb
a/b=sinA/sinB
cosB/cosA=a/b
acosA=bcosB
a[(bb+cc-aa)/2bc] = b[(aa+cc-bb)/2ac]
aa(bb+cc-aa) = bb(aa+cc-bb)
aacc-aaaa=bbcc-bbbb
cc(aa-bb)=(aa-bb)(aa+bb)
aa-bb is not 0 <-- wrong
so cc=aa+bb or a=b