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In any triangleABC, prove that a^(2)=(b...

In any `triangleABC`, prove that `a^(2)=(b+c)^(2) -4b(c)cos^(2)(A/2)`

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`cosA = (b^(2)+c^(2)-a^(2))/(2bc)`
`rArr 2cos^(2)A/2-1=(b^(2)+c^(2)-a^(2))/(2bc)`
`rArr 2cos^(2)A/2 =(b^(2)+c^(2)-a^(2)+2bc)/(2bc)`
`rArr a^(2) =(b+c)^(2) -4bc cos^(2)A/2`
Hence Proved.
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