Geometric Inequality Problem: Prove AD < AC in Triangle ABC

Triangle Inequalities with Interior Points

Choose the correct answer AD<AC AD < AC

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine whether AD is less than AC
00:04 Find the segment AD
00:08 Find AC
00:15 We can observe that AD is part of AC, therefore it must be less than AC
00:18 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Choose the correct answer AD<AC AD < AC

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2

Step-by-step solution

To determine if the inequality AD<AC AD < AC is true, we first consider the configuration given in the problem.

1. The diagram shows triangle ABC ABC , with A A being the vertex and B B and C C lying on the line BC BC , which is the base of the triangle. The vertex D D is placed such that it seems to be an interior point of triangle ABC ABC .

2. Observe that point D D lies on the segment connecting the midpoint of the line BC BC to vertex A A . The vertex C C is at the other end of the line BC BC .

3. Geometrically, since point D D lies inside triangle ABC ABC and not on the boundary of triangle ABC ABC , segment AD AD being inside implies it is shorter than segment AC AC , which extends to the triangular boundary on line BC BC .

4. Therefore, the position of D D suggests that AD AD (an interior segment) is indeed shorter than AC AC (an exterior segment extending from A A to C C ). Hence the inequality AD<AC AD < AC is valid.

Therefore, the given statement AD<AC AD < AC is True.

3

Final Answer

True

Key Points to Remember

Essential concepts to master this topic
  • Triangle Inequality: Interior segments are always shorter than boundary segments
  • Technique: Point D inside triangle ABC means AD<AC AD < AC
  • Check: Interior point creates shorter path than vertex-to-vertex distance ✓

Common Mistakes

Avoid these frequent errors
  • Confusing interior and exterior points
    Don't assume point D is on the boundary of triangle ABC = treating AD as equal to AC! Interior points always create shorter distances to vertices. Always identify whether the point lies inside, outside, or on the triangle boundary.

Practice Quiz

Test your knowledge with interactive questions

Is DE side in one of the triangles?
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FAQ

Everything you need to know about this question

How can I tell if point D is inside triangle ABC?

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Look at the diagram carefully! If point D lies between the triangle's sides without touching any edge, it's an interior point. Interior points are always closer to vertices than boundary points.

Why is AD shorter than AC if both start from point A?

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Think of it like taking a shortcut! Point D is inside the triangle, so the path from A to D is shorter than going all the way to the boundary point C. It's like walking across a field versus walking to the fence.

What if point D was on side BC instead?

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If D were on side BC, then AD AD could still be shorter than AC AC unless D coincides with C. The triangle inequality tells us the shortest path between two points is a straight line.

Can AD ever equal AC in this type of problem?

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Only if point D is exactly at point C! Since the diagram shows D as a separate interior point, AD<AC AD < AC must be true.

How do I prove this without measuring?

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Use the triangle inequality principle: In any triangle, each side is shorter than the sum of the other two sides. Since D is interior, AD represents a 'shortcut' compared to the full side AC.

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