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प्रश्न
In ΔABC, if a = 2, b = 3, c = 4, then prove that the triangle is obtuse angled.
प्रमेय
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उत्तर
Given: a = 2, b = 3, c = 4
∴ Side AB is the largest.
Hence, ∠C is the largest angle.
By cosine rule, cos C = `(a^2 + b^2 - c^2)/(2ab)`
∴ cos C = `(4 + 9 - 16)/(2(2)(3))`
= `(-3)/12`
= `- 1/4`
Since cos C is negative, ∠C is obtuse.
∴ ΔABC is an obtuse angled triangle.
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