1.

In any ` A B C`, prove that:`2{asin^2C/2+csin^2A/2}=a+c-b`

Answer» We know, `2sin^2x = 1-cos2x`
`:. L.H.S. = 2(asin^2(C/2)+csin^2(A/2))`
`=a(1-cosC)+c(1-cosA)`
`=a+c -(acosC+c cosA)`
From projection formula,
`b = (acosC+c cosA)`
`:. a+c -(acosC+c cosA) = a+c - b = R.H.S.`


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