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Mathematics

Assertion (A): In a Δ ABC, if D is a point on the side BC such that AD divides BC in ratio AB : AC, then AD is the bisector of ∠A.

Reason (R): The internal bisector of an angle of a triangle divides the opposite side internally in the ratio of the sides containing the angle.

  1. Assertion (A) is true, but Reason (R) is false.

  2. Assertion (A) is false, but Reason (R) is true.

  3. Both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct reason for Assertion (A).

  4. Both Assertion (A) and Reason (R) are correct, and Reason (R) is incorrect reason for Assertion (A).

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Answer

By angle bisector theorem,

The internal bisector of an angle of a triangle divides the opposite side internally in the ratio of the sides containing the angle.

In a Δ ABC, if D is a point on the side BC such that AD divides BC in ratio AB : AC, then AD is the bisector of ∠A. Reason : The internal bisector of an angle of a triangle divides the opposite side internally in the ratio of the sides containing the angle. Similarity, ML Aggarwal Understanding Mathematics Solutions ICSE Class 10.

In a ΔABC, if AD is the internal angle bisector of ∠A, then it divides the opposite side BC in the ratio:

BDDC=ABAC\dfrac{BD}{DC} = \dfrac{AB}{AC}

So, reason (R) is true.

In a ΔABC, if D is a point on the side BC such that AD divides BC in ratio AB : AC, then AD is the bisector of ∠A.

This is the converse of the Angle Bisector Theorem.

So, assertion (A) is true.

Thus, both Assertion (A) and Reason (R) are correct, and Reason (R) is the correct reason for Assertion (A).

Hence, option 3 is the correct option.

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