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In a Delta A B C , prove the following ...

In a ` Delta A B C ,` prove the following : `\ a(cos B+cos C-1)+b(cos C+cos A-1)+c(cos A+cos B-1)=0` .

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In any `triangle {ABC}`, we have
`` a=b cos C+c cos B
`` `` b=c cos A+a cos C
`` `c=a cos B+b cos A`
...
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