Difficulty: Medium
Correct Answer: Both 1 and 2
Explanation:
Introduction / Context:
This is a conceptual geometry question that asks you to judge the validity of two statements about triangles. Both statements involve inequalities between side lengths and related segments such as medians and line segments drawn from a vertex to a point on the opposite side. Such questions are common in aptitude and competitive exams because they test understanding of triangle inequality and properties of medians without requiring numerical calculation.
Given Data / Assumptions:
- We consider a general triangle with sides of positive length.
- Statement 1: The perimeter of a triangle is greater than the sum of its three medians.
- Statement 2: For triangle ABC and any point D on side BC, AB + BC + CA is greater than 2AD.
- No special type of triangle is assumed unless implied by standard geometry (triangle is non degenerate).
Concept / Approach:
For Statement 1, we use a known inequality involving medians: in any triangle, the sum of the medians is less than the perimeter. This follows from the fact that each median is shorter than the average of the two sides it connects in an indirect way and from geometric constructions that compare medians with sides. For Statement 2, we apply the triangle inequality carefully to two smaller triangles formed when we choose a point D on side BC. By writing the triangle inequality in triangles ABD and ACD and then adding the inequalities, we derive AB + BC + CA greater than 2AD.
Step-by-Step Solution:
Step 1: Let the triangle have sides a, b, c and medians ma, mb, mc drawn to those sides.
Step 2: It is a known geometric result that ma + mb + mc is less than a + b + c. Geometrically, one way to see this is by constructing the triangle formed by the three medians and comparing its perimeter to the original triangle, or by more advanced inequality proofs. The key is that each median is always less than half the sum of the two sides that form the endpoints of the median.
Step 3: Since a + b + c is the perimeter of the triangle, and ma + mb + mc is less than this perimeter, Statement 1, which claims that the perimeter is greater than the sum of medians, is correct.
Step 4: For Statement 2, consider triangle ABC and let D be any point on side BC.
Step 5: In triangle ABD, the triangle inequality gives AB + BD greater than AD.
Step 6: In triangle ACD, the triangle inequality gives AC + CD greater than AD.
Step 7: Add these two inequalities: (AB + BD) + (AC + CD) greater than AD + AD which simplifies to AB + AC + (BD + CD) greater than 2AD.
Step 8: Since D lies on BC, BD + CD equals BC. So we have AB + AC + BC greater than 2AD.
Step 9: Therefore Statement 2 is also correct.
Verification / Alternative check:
You can test Statement 2 with a simple numerical example. Consider a right triangle with AB = 3, AC = 4, BC = 5. Choose D as the midpoint of BC so that BD = CD = 2.5. Compute AD using the distance formula or Pythagoras in coordinates. You will find that AB + BC + CA is comfortably larger than 2AD, confirming the inequality numerically. Since the proof using triangle inequalities was general, the statement holds for any choice of D on BC.
Why Other Options Are Wrong:
Option 1 only would mean Statement 2 is false, but we have shown that the triangle inequality directly proves Statement 2.
Option 2 only would mean Statement 1 is false, which contradicts the known result that the sum of medians is always less than the perimeter of the triangle.
Option Neither 1 nor 2 is incorrect because both statements are valid geometric facts.
Common Pitfalls:
Students sometimes misremember properties of medians and may think that the sum of medians can exceed the perimeter, which is not true. Another common mistake is to apply the triangle inequality incorrectly, for example writing AB + AC greater than BC + AD incorrectly or mixing up which segments belong to which triangle. It is important to write triangle inequalities separately for each triangle, then add them carefully. Also, some learners mistakenly think that D must be the midpoint of BC; however, Statement 2 holds for any point D on BC, not just the midpoint.
Final Answer:
Both statements are correct, so the right choice is Both 1 and 2.
Discussion & Comments