MHB Is there a formula for finding the perimeter of a triangle with known vertices?

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To find the perimeter of triangle ABC with vertices A(1, 1), B(9, 3), and C(3, 5), the distance formula is used to calculate the lengths of each side, which are then summed. For the triangle formed by the midpoints of the sides, the midpoints of AB, BC, and CA must be calculated, followed by applying the same distance formula to find that perimeter. The ratio of the two perimeters can be expressed as r = (perimeter part 1)/(perimeter part 2). The Triangle Midpoint Theorem provides a geometric solution for the ratio without needing to compute the perimeters directly. The discussion concludes with a reference to previously posted questions on the same topic, indicating progress in understanding.
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The vertices of triangle ABC are A(1, 1), B(9, 3), and C(3, 5).

1. Find the perimeter of triangle ABC.

I must use the distance formula for points to find the individual lengths. I then must add all 3 lengths to find the perimeter. Correct?

2. Find the perimeter of the triangle that is formed by joining the midpoints of the three sides of triangle ABC.

I MUST find the midpoint of AB, BC, and BC. I then repeat the same steps for part 1 above. Correct?

3. Compute the ratio of the perimeter on part 1 to the perimeter in part b.

Let r = ratio

r = (perimeter part 1)/(perimeter part 2)

Is this what I must solve for part 3?

4. What theorem from geometry provides the answer for part 3 without using the results in part 1 and 2.

I need help with part 4.
 
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4. The Triangle Midpoint theorem.
 
You may wish to review these threads, as they deal with the same triangle and perimeter:

  • https://mathhelpboards.com/pre-calculus-21/triangle-abc-22202.html
  • https://mathhelpboards.com/pre-calculus-21/perimeter-triangle-abc-21551.html
  • https://mathhelpboards.com/pre-calculus-21/perimeter-triangle-abc-21111.html
 
MarkFL said:
You may wish to review these threads, as they deal with the same triangle and perimeter:

  • http://mathhelpboards.com/pre-calculus-21/triangle-abc-22202.html
  • http://mathhelpboards.com/pre-calculus-21/perimeter-triangle-abc-21551.html
  • http://mathhelpboards.com/pre-calculus-21/perimeter-triangle-abc-21111.html

I forgot that I had posted the same question some time ago. Good. I can move on in the textbook.
 
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