Difference between revisions of "2016 AMC 12A Problems/Problem 15"
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We can use the Pythagorean theorem to find that the lengths are <math>3,5,\sqrt{36+16\sqrt{3}}</math>. If we apply Heron’s, we know that it must be the sum (or difference) of two or more square roots, by instinct. This means that <math>\boxed{\textbf{(D)} \sqrt{6}-\sqrt{2}}</math> is the answer. | We can use the Pythagorean theorem to find that the lengths are <math>3,5,\sqrt{36+16\sqrt{3}}</math>. If we apply Heron’s, we know that it must be the sum (or difference) of two or more square roots, by instinct. This means that <math>\boxed{\textbf{(D)} \sqrt{6}-\sqrt{2}}</math> is the answer. | ||
+ | |||
+ | ==Solution 6 (Educated Guess)== | ||
+ | |||
+ | Like Solution 1, we can use the Pythagorean theorem to find <math>P'Q'</math> and <math>Q'R'</math>, which are <math>2\sqrt2</math> and <math>2\sqrt6</math> respectively. Since the only answer choice that has <math>\sqrt2</math> and <math>\sqrt6</math> is <math>D</math>, we can make an educated guess that <math>\boxed{\textbf{(D)} \sqrt{6}-\sqrt{2}}</math> is the answer. | ||
+ | |||
==Solution 6 (Educated Guess)== | ==Solution 6 (Educated Guess)== |
Revision as of 23:33, 24 August 2024
Contents
Problem
Circles with centers and
, having radii
and
, respectively, lie on the same side of line
and are tangent to
at
and
, respectively, with
between
and
. The circle with center
is externally tangent to each of the other two circles. What is the area of triangle
?
Solution 1
Notice that we can find in two different ways:
and
Since we want
we use the latter method, so we have
. Additionally,
. Therefore,
. Similarly,
. We can calculate
easily because
.
.
Plugging into first equation, the two sums of areas, so therefore
Solution 2
Use the Shoelace Theorem.
Let the center of the first circle of radius 1 be at .
Draw the trapezoid and using the Pythagorean Theorem, we get that
so the center of the second circle of radius 2 is at
.
Draw the trapezoid and using the Pythagorean Theorem, we get that
so the center of the third circle of radius 3 is at
.
Now, we may use the Shoelace Theorem!
Solution 3
and
because they are the sum of two radii.
and
, the difference of the radii. Using pythagorean theorem, we find that
and
are
and
,
.
Draw a perpendicular from to line
, then we can use the Pythagorean theorem to find
.
. We get
To make our calculations easier, let . The semi-perimeter of our triangle is
. Symbolize the area of the triangle with
. Using Heron's formula, we have
We can remove the outer root of a.
We solve the nested root. We want to turn into the square of something. If we have
, then we get
Solving the system of equations, we get
and
. Alternatively, you can square all the possible solutions until you find one that is equal to
~ZericH
Solution 4
The above diagram can be achieved relatively simply using basic knowledge of the Pythagorean theorem and the fact that the radius from the center to the point of tangency is perpendicular to the tangent line. From there, observe that
can be calculated in two ways:
and
. Solving, we get:
- ColtsFan10, diagram partially borrowed from Solution 1
Solution 5 (Heron’s)
We can use the Pythagorean theorem to find that the lengths are . If we apply Heron’s, we know that it must be the sum (or difference) of two or more square roots, by instinct. This means that
is the answer.
Solution 6 (Educated Guess)
Like Solution 1, we can use the Pythagorean theorem to find and
, which are
and
respectively. Since the only answer choice that has
and
is
, we can make an educated guess that
is the answer.
Solution 6 (Educated Guess)
Like Solution 1, we can use the Pythagorean theorem to find and
, which are
and
respectively. Since the only answer choice that has
and
is
, we can make an educated guess that
is the answer.
Video Solutions
https://www.youtube.com/watch?v=sWurLJqf02Y ~by Punxsutawney Phil
https://www.youtube.com/watch?v=UanfIBpDTh8&ab_channel=ArtofProblemSolving ~by the official Art of Problem Solving channel on YouTube
See Also
2016 AMC 10A (Problems • Answer Key • Resources) | ||
Preceded by Problem 20 |
Followed by Problem 22 | |
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 10 Problems and Solutions |
2016 AMC 12A (Problems • Answer Key • Resources) | |
Preceded by Problem 14 |
Followed by Problem 16 |
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.