Geometry set
20 problems, difficulty 2–4, one per topic where possible
- 1.2006 AMC 10B #5
A rectangle and a rectangle are contained within a square without overlapping at any point, and the sides of the square are parallel to the sides of the two given rectangles. What is the smallest possible area of the square?
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- 2.2011 AMC 10B #9
The area of is one third of the area of . Segment is perpendicular to segment . What is ?

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- 3.2011 AMC 10B #7
The sum of two angles of a triangle is of a right angle, and one of these two angles is larger than the other. What is the degree measure of the largest angle in the triangle?
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- 4.2015 AMC 10B #12
For how many integers is the point inside or on the circle of radius centered at ?
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- 5.2016 AMC 10A #16
A triangle with vertices , , and is reflected about the -axis, then the image is rotated counterclockwise about the origin by to produce . Which of the following transformations will return to ?
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counterclockwise rotation about the origin by .
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clockwise rotation about the origin by .
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reflection about the -axis
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reflection about the line $y = x
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reflection about the -axis.
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- 6.2025 AMC 10A #3
How many isosceles triangles are there with positive area whose side lengths are all positive integers and whose longest side has length ?
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- 7.2010 AMC 10A #16
Nondegenerate has integer side lengths, is an angle bisector, , and . What is the smallest possible value of the perimeter?
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- 8.2011 AMC 10B #17
In the given circle, the diameter is parallel to , and is parallel to . The angles and are in the ratio . What is the degree measure of angle ?

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- 9.2012 AMC 10B #19
In rectangle , , , and is the midpoint of . Segment is extended 2 units beyond to point , and is the intersection of and . What is the area of ?
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- 10.2013 AMC 10B #16
In triangle , medians and intersect at , , , and . What is the area of ?
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- 11.2014 AMC 10A #13
Equilateral has side length , and squares , , lie outside the triangle. What is the area of hexagon ?

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- 12.2018 AMC 10A #16
Right triangle has leg lengths and . Including and , how many line segments with integer length can be drawn from vertex to a point on hypotenuse ?
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- 13.2010 AMC 10A #20
A fly trapped inside a cubical box with side length meter decides to relieve its boredom by visiting each corner of the box. It will begin and end in the same corner and visit each of the other corners exactly once. To get from a corner to any other corner, it will either fly or crawl in a straight line. What is the maximum possible length, in meters, of its path?
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- 14.2011 AMC 10B #25
Let be a triangle with sides and . For , if and and are the points of tangency of the incircle of to the sides and respectively, then is a triangle with side lengths and if it exists. What is the perimeter of the last triangle in the sequence ?
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- 15.2015 AMC 10A #21
Tetrahedron has , , , , , and . What is the volume of the tetrahedron?
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- 16.2017 AMC 10A #21
A square with side length is inscribed in a right triangle with sides of length , , and so that one vertex of the square coincides with the right-angle vertex of the triangle. A square with side length is inscribed in another right triangle with sides of length , , and so that one side of the square lies on the hypotenuse of the triangle. What is ?
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- 17.2018 AMC 10A #21
Which of the following describes the set of values of for which the curves and in the real -plane intersect at exactly points?
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- 18.2019 AMC 10A #21
A sphere with center has radius 6. A triangle with sides of length , , and is situated in space so that each of its sides are tangent to the sphere. What is the distance between and the plane determined by the triangle?
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- 19.2020 AMC 10A #23
Let be the triangle in the coordinate plane with vertices and Consider the following five isometries (rigid transformations) of the plane: rotations of and counterclockwise around the origin, reflection across the -axis, and reflection across the -axis. How many of the sequences of three of these transformations (not necessarily distinct) will return to its original position? (For example, a rotation, followed by a reflection across the -axis, followed by a reflection across the -axis will return to its original position, but a rotation, followed by a reflection across the -axis, followed by another reflection across the -axis will not return to its original position.)
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- 20.2021 AMC 10A #21
Let be an equiangular hexagon. The lines and determine a triangle with area , and the lines and determine a triangle with area . The perimeter of hexagon can be expressed as , where and are positive integers and is not divisible by the square of any prime. What is ?
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Answers
| # | Answer | Topic and the idea it turns on |
|---|---|---|
| 1 | B | Geometric Optimization — Total area 18 rules out a 4 by 4 square; placing the rectangles side by side (widths 2 + 3, heights 3 and 4) fits in 5 by 5. |
| 2 | D | Similar & Congruent Triangles — Triangle EBD shares angle B with ABC and is right-angled, so it is similar; area ratio 1/3 means side ratio 1/sqrt(3), and BD corresponds to BC = 4. |
| 3 | B | Angles & Polygons — The two angles total 108 degrees, so they are 39 and 69, and the third angle 180 - 108 = 72 is the largest. |
| 4 | A | Coordinate Geometry — Plug (x, -x) into the circle inequality; the cross terms cancel and it collapses to x^2 <= 25, so x runs from -5 to 5. |
| 5 | D | Transformations & Symmetry — Track (x, y): the reflection gives (x, -y), the rotation then gives (y, x), so the combined map is reflection over y = x, its own inverse. |
| 6 | D | Triangles: Area & Pythagorean — Split on where the equal pair sits: (2025, 2025, b) needs only 1 <= b <= 2025, while (a, a, 2025) needs 2a > 2025, so a >= 1013. |
| 7 | B | Triangle Centers & Cevians — The angle bisector theorem forces AB : BC = 3 : 8, so sides are 3m, 8m, 11; m = 1 is degenerate, m = 2 gives 6, 16, 11. |
| 8 | C | Circles — Angle EAB is 90 (inscribed in a semicircle), so angle ABE is 50; parallels carry it to angle BED, and cyclic quadrilateral EDCB gives angle BCD = 130. |
| 9 | C | Quadrilaterals & Polygon Areas — BFDG is a trapezoid with parallel sides BF and GD; similar triangles EBF and EAD give BF = 7.5, and GD = 15 with height 6. |
| 10 | B | Triangle Centers & Cevians — 1.5, 2, 2.5 is a right triangle, so the medians are perpendicular; the centroid's 2:1 ratio gives AD = 6, CE = 4.5, and AEDC has area half their product. |
| 11 | C | Quadrilaterals & Polygon Areas — The hexagon splits into the triangle, three unit squares, and three gap triangles with unit legs and a 120-degree apex, each having the same area as the equilateral triangle. |
| 12 | D | Triangles: Area & Pythagorean — Sliding along AC, the distance from B falls from 20 to the altitude 420/29 (about 14.5), then rises to 21, hitting each integer once per side. |
| 13 | D | Geometric Optimization — Each corner has one space diagonal and the tour uses two legs per corner, so at most 4 legs are space diagonals; the rest can be face diagonals. |
| 14 | D | Circles — Tangent lengths are s - a, so sides x-1, x, x+1 become x/2-1, x/2, x/2+1; the middle side halves until it drops below 2. |
| 15 | C | Solid Geometry — Faces ABC and ABD are congruent 3-4-5 right triangles sharing hypotenuse AB; their altitudes to AB meet at the same foot, and CD = (12/5)sqrt2 makes them perpendicular. |
| 16 | D | Similar & Congruent Triangles — Each square cuts off triangles similar to the 3-4-5; the corner square gives x = 12/7, and the hypotenuse splits as 4y/3 + y + 3y/4 = 5. |
| 17 | E | Coordinate Geometry — Substituting x^2 = y + a gives a quadratic in y whose root y = -a is the lone axis point; the other root needs 2a - 1 > 0. |
| 18 | D | Solid Geometry — The sphere meets the triangle's plane in a circle tangent to all three sides, the incircle of radius 4; then distance = sqrt(6^2 - 4^2). |
| 19 | A | Transformations & Symmetry — T has no symmetry, so the composite must be the identity; reflections flip orientation, so there are 0 or 2 of them, and each case gives 6 sequences. |
| 20 | C | Angles & Polygons — Both triangles are equilateral (120-degree angles leave 60-degree corners); one has side AB+BC+FA, the other CD+DE+EF, so the perimeter is their side lengths summed. |