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M is a point on side BC of a triangle ABC such that AM is the bisector of ∠BAC. Is it true to say that perimeter of the triangle is greater than 2 AM? Give reason for your answer.

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Question

M is a point on side BC of a triangle ABC such that AM is the bisector of ∠BAC. Is it true to say that perimeter of the triangle is greater than 2 AM? Give reason for your answer.

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Solution

Yes, In ΔABC, M is a point of side BC such that AM is the bisector of ∠BAC.

In ΔABM, AB + BM > AM  ...(i) [Sum of two sides of a triangle is greater than the third side] 

In ΔACM, AC + CM > AM  ...(ii) [Sum of two sides of a triangle is greater than the third side] 


On adding equations (i) and (ii), we get

(AB + BM + AC + CM) > 2AM

⇒ (AB + BM + MC + AC) > 2AM

⇒ AB + BC + AC > 2AM   ...[∵ BC = BM + MC]

∴ Perimeter of ΔABC > 2AM

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Chapter 7: Triangles - Exercise 7.2 [Page 65]

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NCERT Exemplar Mathematics Exemplar [English] Class 9
Chapter 7 Triangles
Exercise 7.2 | Q 10. | Page 65

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