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JEE MainMathematicsModerate

In Δ\DeltaABC, if (a + b + c) (a - b + c) = 3ac, then

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(a + c)^2 - b^2 = 3ac
⇒a2+c2−b22ac=12⇒cosB=12\Rightarrow \frac{a^{2} + c^{2} - b^{2}}{2ac} = \frac{1}{2} \Rightarrow cosB = \frac{1}{2}
⇒\Rightarrow B = 60º

Source: Grass-G / M-24 Mathematics Paper 31 Dec.docx

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