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Sum of two sides of a triangle is greater than the third side. R.S. Aggarwal Mathematics Solutions ICSE Class 9.

Assertion (A): In △ABC, D is a point on side BC. AB + BC + AC > 2AD

Reason (R): Sum of two sides of a triangle is greater than the third side.

  1. A is true, R is false

  2. A is false, R is true

  3. Both A and R are true

  4. Both A and R are false

Triangles

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Answer

We know that,

Sum of two sides of a triangle is greater than the third side is fundamental property of triangle.

∴ Reason (R) is true.

In △ABD,

⇒ AB + BD > AD …(1) [Sum of any two sides of triangle is greater than the third side]

In △ADC,

⇒ AC + CD > AD …(2) [Sum of any two sides of triangle is greater than the third side]

Adding eq.(1) and (2), we have:

⇒ AB + BD + AC + CD > AD + AD

⇒ AB + AC + BD + CD > 2AD

⇒ AB + AC + BC > 2AD

∴ Assertion (A) is true.

Hence, option 3 is the correct option.

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