Difference between revisions of "2019 AMC 10B Problems/Problem 8"
Sevenoptimus (talk | contribs) (Fixed problem statement) |
Sevenoptimus (talk | contribs) (Improved grammar, formatting, and readability, and removed irrelevant attribution) |
||
Line 20: | Line 20: | ||
==Solution== | ==Solution== | ||
− | We notice that the square can be split into <math>4</math> congruent smaller squares with the altitude of the equilateral triangle being the side of | + | We notice that the square can be split into <math>4</math> congruent smaller squares, with the altitude of the equilateral triangle being the side of this smaller square. Therefore, the area of each shaded part that resides within a square is the total area of the square subtracted from each triangle (which has already been split in half). |
− | When we split an equilateral triangle in half, we get | + | When we split an equilateral triangle in half, we get two <math>30^{\circ}-60^{\circ}-90^{\circ}</math> triangles. Therefore, the altitude, which is also the side length of one of the smaller squares, is <math>\sqrt{3}</math>. We can then compute the area of the two triangles as <math>2 \cdot \frac{1 \cdot \sqrt{3}}{2} = \sqrt{3}</math>. |
− | + | The area of the each small squares is the square of the side length, i.e. <math>\left(\sqrt{3}\right)^2 = 3</math>. Therefore, the area of the shaded region in each of the four squares is <math>3 - \sqrt{3}</math>. | |
− | + | Since there are <math>4</math> of these squares, we multiply this by <math>4</math> to get <math>4\left(3 - \sqrt{3}\right) = \boxed{\textbf{(B) } 12 - 4\sqrt{3}}</math> as our answer. | |
− | |||
− | |||
− | |||
− | |||
==See Also== | ==See Also== |
Revision as of 20:38, 17 February 2019
Problem
The figure below shows a square and four equilateral triangles, with each triangle having a side lying on a side of the square, such that each triangle has side length and the third vertices of the triangles meet at the center of the square. The region inside the square but outside the triangles is shaded. What is the area of the shaded region?
Solution
We notice that the square can be split into congruent smaller squares, with the altitude of the equilateral triangle being the side of this smaller square. Therefore, the area of each shaded part that resides within a square is the total area of the square subtracted from each triangle (which has already been split in half).
When we split an equilateral triangle in half, we get two triangles. Therefore, the altitude, which is also the side length of one of the smaller squares, is
. We can then compute the area of the two triangles as
.
The area of the each small squares is the square of the side length, i.e. . Therefore, the area of the shaded region in each of the four squares is
.
Since there are of these squares, we multiply this by
to get
as our answer.
See Also
2019 AMC 10B (Problems • Answer Key • Resources) | ||
Preceded by Problem 7 |
Followed by Problem 9 | |
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 |
The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.