Difference between revisions of "2002 AMC 12B Problems/Problem 23"
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== Solution == | == Solution == | ||
− | === Solution 1 === | + | === Solution 1: Pythagorean Theorem === |
<asy> | <asy> | ||
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~greenturtle 11/28/2017 | ~greenturtle 11/28/2017 | ||
− | === Solution 2 === | + | === Solution 2: Law of Cosines === |
[[Image:2002_12B_AMC-23.png]] | [[Image:2002_12B_AMC-23.png]] | ||
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Hence <math>a = \frac{1}{\sqrt{2}}</math> and <math>BC = 2a = \sqrt{2} \Rightarrow \mathrm{(C)}</math>. | Hence <math>a = \frac{1}{\sqrt{2}}</math> and <math>BC = 2a = \sqrt{2} \Rightarrow \mathrm{(C)}</math>. | ||
− | === Solution 3 === | + | === Solution 3: Stewart's Theorem === |
From [[Stewart's Theorem]], we have <math>(2)(1/2)a(2) + (1)(1/2)a(1) = (a)(a)(a) + (1/2)a(a)(1/2)a.</math> Simplifying, we get <math>(5/4)a^3 = (5/2)a \implies (5/4)a^2 = 5/2 \implies a^2 = 2 \implies a = \boxed{\sqrt{2}}.</math> | From [[Stewart's Theorem]], we have <math>(2)(1/2)a(2) + (1)(1/2)a(1) = (a)(a)(a) + (1/2)a(a)(1/2)a.</math> Simplifying, we get <math>(5/4)a^3 = (5/2)a \implies (5/4)a^2 = 5/2 \implies a^2 = 2 \implies a = \boxed{\sqrt{2}}.</math> | ||
- awu2014 | - awu2014 | ||
− | === Solution 4 | + | === Solution 4: Pappus's Median Theorem === |
− | There is a theorem in geometry known as Pappus's Median Theorem. It states that if you have <math>\triangle{ABC}</math>, and you draw a median from point <math>A</math> to side <math>BC</math> (label this as <math>M</math>), then: <math>(AM)^2 = \dfrac{2(b^2) + 2(c^2) - (a^2)}{4}</math>. Note that <math>b</math> is the length of side <math>\overline{AC}</math>, <math>c</math> is the length of side <math>\overline{AB}</math>, and <math>a</math> is length of side <math>\overline{BC}</math>. Let <math>MB = MC = x</math>. Then <math>AM = 2x</math>. Now, we can plug into the formula given above: <math>AM = 2x</math>, <math>b = 2</math>, <math>c = 1</math>, and <math>a = 2x</math>. After some simple algebra, we find <math>x = \dfrac{\sqrt{2}}{2}</math>. Then, <math>BC = \sqrt{2}</math>. | + | There is a theorem in geometry known as Pappus's Median Theorem. It states that if you have <math>\triangle{ABC}</math>, and you draw a median from point <math>A</math> to side <math>BC</math> (label this as <math>M</math>), then: <math>(AM)^2 = \dfrac{2(b^2) + 2(c^2) - (a^2)}{4}</math>. Note that <math>b</math> is the length of side <math>\overline{AC}</math>, <math>c</math> is the length of side <math>\overline{AB}</math>, and <math>a</math> is length of side <math>\overline{BC}</math>. Let <math>MB = MC = x</math>. Then <math>AM = 2x</math>. Now, we can plug into the formula given above: <math>AM = 2x</math>, <math>b = 2</math>, <math>c = 1</math>, and <math>a = 2x</math>. After some simple algebra, we find <math>x = \dfrac{\sqrt{2}}{2}</math>. Then, <math>BC = \boxed{\sqrt{2}} \implies \boxed{C}</math>. |
-Flames | -Flames | ||
+ | |||
+ | Note: Pappus's Median Theorem is just a special case of Stewart's Theorem, with <math>m = n</math>. ~Puck_0 | ||
+ | aka Apollonius' Theorem - Orion 2010 | ||
===Video Solution by TheBeautyofMath=== | ===Video Solution by TheBeautyofMath=== |
Latest revision as of 12:53, 9 July 2024
Contents
Problem
In , we have and . Side and the median from to have the same length. What is ?
Solution
Solution 1: Pythagorean Theorem
Let be the foot of the altitude from to extended past . Let and . Using the Pythagorean Theorem, we obtain the equations
Subtracting equation from and , we get
Then, subtracting from and rearranging, we get , so
~greenturtle 11/28/2017
Solution 2: Law of Cosines
Let be the foot of the median from to , and we let . Then by the Law of Cosines on , we have
Since , we can add these two equations and get
Hence and .
Solution 3: Stewart's Theorem
From Stewart's Theorem, we have Simplifying, we get - awu2014
Solution 4: Pappus's Median Theorem
There is a theorem in geometry known as Pappus's Median Theorem. It states that if you have , and you draw a median from point to side (label this as ), then: . Note that is the length of side , is the length of side , and is length of side . Let . Then . Now, we can plug into the formula given above: , , , and . After some simple algebra, we find . Then, .
-Flames
Note: Pappus's Median Theorem is just a special case of Stewart's Theorem, with . ~Puck_0 aka Apollonius' Theorem - Orion 2010
Video Solution by TheBeautyofMath
~IceMatrix
See also
2002 AMC 12B (Problems • Answer Key • Resources) | |
Preceded by Problem 22 |
Followed by Problem 24 |
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
All AMC 12 Problems and Solutions |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.