1.

In any ` DeltaABC`, prove that:`(sinB)/(sinC)=(c-acosB)/(b-acosC)`

Answer» `R.H.S. = (c-acosB)/(b-acosC)`
From projection formulas,
`c = acosB + bcosA`
`b = acosC+c cosA`
`:.(c-acosB)/(b-acosC) = (acosB + bcosA-acosB)/(acosC+c cosA-acosC)`
`=(bcosA)/(c cosA)`
`=b/c`
`L.H.S. = sin B/sinC`
From Sine formulas,`sinA = ka, sinB = kb, sin C = kc`
`:. sin B/sinC = (kb)/(kc) = b/c`
`:. L.H.S. = R.H.S.`


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