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In a A B C , if /B=60^@ , prove that (a...

In a ` A B C` , if `/_B=60^@` , prove that `(a+b+c)(a-b+c)=3c a`

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Given `/_B=60^0`
We know that by cosine formula
`2bc cosA=b^2+c^2-a^2...(i)`
`2ab cosC=a^2+b^2-c^2....(ii)`
`2ac cosB=a^2+c^2-b^2....(iii)`
so,By using formula (iii) we get
`2ac cosB=a^2+c^2-b^2`
`=>cos 60^@=(a^2+c^2-b^2)/(2ac) [Given /_B=60^0]`
...
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