Chứng minh rằng tam giác cân khi và chỉ khi:
$a.\sin (B-C)+b.\sin (C-A)=0$
$a.\sin (B-C)+b.\sin (C-A)=0$
Started By quanghao98, 17-04-2014 - 18:07
#1
Posted 17-04-2014 - 18:07
quanghao98
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I've got a dream,the day,I'll catch it,can do...don't never give up...if I dream,I can do it.
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#2
Posted 17-04-2014 - 19:48
Tran Nho Duc
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Chứng minh rằng tam giác cân khi và chỉ khi:
$a.\sin (B-C)+b.\sin (C-A)=0$
" Even if there was no Gravity on Earth, I'd still fall for you. "
Nunmul
#3
Posted 17-04-2014 - 19:53
Tran Nho Duc
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$a.sin(B-C)+b.sin(C-A)=0\Leftrightarrow a.(sinB.cosC-sinC.cosB)+b(sinC.cosA-sinA.cosC)=0\Leftrightarrow a.\frac{1}{2R}(b.cosC-c.cosB)+b.\frac{1}{2R}(c.cosA-a.cosC)=0\Leftrightarrow ab.cosC-ac.cosB+bc.cosA-ab.cosC=0\Leftrightarrow .....\Leftrightarrow a=b$
" Even if there was no Gravity on Earth, I'd still fall for you. "
Nunmul
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