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| ==Solution 1== | | ==Solution 1== |
− | Let G be the midpoint B and C
| + | The area of trapezoid <math>CBFE</math> is <math>\frac{1+3}2\cdot 4=8</math>. Next, we find the height of each triangle to calculate their area. The two non-colored isosceles triangles are similar, and are in a <math>3:1</math> ratio by AA similarity (alternate interior and vertical angles) so the height of the larger is <math>3,</math> while the height of the smaller one is <math>1.</math> Thus, their areas are <math>\frac12</math> and <math>\frac92</math>. Subtracting these areas from the trapezoid, we get <math>8-\frac12-\frac92 =\boxed3</math>. Therefore, the answer to this problem is <math>\boxed{\textbf{(C) }3}</math> |
− | Draw H, J, K beneath C, G, B, respectively.
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− | <asy>
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− | draw((0,0)--(3,0)--(3,4)--(0,4)--(0,0)--(2,4)--(3,0));
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− | draw((3,0)--(1,4)--(0,0));
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− | fill((0,0)--(1,4)--(1.5,3)--cycle, grey);
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− | fill((3,0)--(2,4)--(1.5,3)--cycle, grey);
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− | draw((1,0)--(1,4));
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− | draw((1.5,0)--(1.5,4));
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− | draw((2,0)--(2,4));
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− | label("$A$",(3.05,4.2));
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− | label("$B$",(2,4.2));
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− | label("$C$",(1,4.2));
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− | label("$D$",(0,4.2));
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− | label("$E$", (0,-0.2));
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− | label("$F$", (3,-0.2));
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− | label("$G$", (1.5, 4.2));
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− | label("$H$", (1, -0.2));
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− | label("$J$", (1.5, -0.2));
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− | label("$K$", (2, -0.2));
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− | label("$1$", (0.5, 4), N);
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− | label("$1$", (2.5, 4), N);
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− | label("$4$", (3.2, 2), E);
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− | </asy>
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− | Let us take a look at rectangle CDEH. I have labeled E' for convenience. First of all, we can see that EE'H and CE'B are similar triangles because all their three angles are the same. Furthermore, since EH=CB, we can confirm that EE'H and CE'B are identical triangles. Thus, CE'=E'H, which is half of CH.
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− | <asy>
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− | fill((0,0)--(1,4)--(1,2)--cycle, grey);
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− | draw((0,0)--(1,0)--(1,4)--(0,4)--(0,0));
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− | draw((0,0)--(1,4)--(1,2)--(0,0));
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− | label("$C$",(1,4.2));
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− | label("$D$",(0,4.2));
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− | label("$E$", (0,-0.2));
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− | label("$H$", (1, -0.2));
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− | label("$E'$", (1.2, 2));
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− | </asy>
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− | Then we can see that CEE' has <math>\frac{1}{4}</math> the area of CDEH because it has half the base and the same height. Similarly, the shaded regions in CGJH, BGJK, and ABKF all have <math>\frac{1}{4}</math> the area of their rectangle. So, the total shaded region is just <math>\frac{1}{4}</math> the area of the total region, or <math>\frac{1}{4} \times 3 \times 4</math>, or <math>\boxed{\textbf{(C) }3}</math>
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− | | |
− | ==Solution 2==
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− | The area of trapezoid <math>CBFE</math> is <math>\frac{1+3}2\cdot 4=8</math>. Next, we find the height of each triangle to calculate their area. The triangles are similar, and are in a <math>3:1</math> ratio by AA similarity (alternate interior and vertical angles) so the height of the largere is <math>3,</math> while the height of the smaller one is <math>1.</math> Thus, their areas are <math>\frac12</math> and <math>\frac92</math>. Subtracting these areas from the trapezoid, we get <math>8-\frac12-\frac92 =\boxed3</math>. Therefore, the answer to this problem is <math>\boxed{\textbf{(C) }3}</math> | |
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− | ==Solution 3 (Coordinate Geometry)==
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− | Set coordinates to the points:
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− | Let <math>E=(0,0)</math>, <math>F=(3,0)</math>
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− | <asy>
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− | draw((0,0)--(3,0)--(3,4)--(0,4)--(0,0)--(2,4)--(3,0));
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− | draw((3,0)--(1,4)--(0,0));
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− | fill((0,0)--(1,4)--(1.5,3)--cycle, black);
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− | fill((3,0)--(2,4)--(1.5,3)--cycle, black);
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− | label(scale(0.7)*"$A(3,4)$",(3.25,4.2));
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− | label(scale(0.7)*"$B(2,4)$",(2.1,4.2));
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− | label(scale(0.7)*"$C(1,4)$",(0.9,4.2));
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− | label(scale(0.7)*"$D(0,4)$",(-0.3,4.2));
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− | label(scale(0.7)*"$E(0,0)$", (0,-0.2));
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− | label(scale(0.7)*"$Z(\frac{3}{2},3)$", (1.5,1.8));
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− | label(scale(0.7)*"$F(3,0)$", (3,-0.2));
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− | label(scale(0.7)*"$1$", (0.3, 4), N);
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− | label(scale(0.7)*"$1$", (1.5, 4), N);
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− | label(scale(0.7)*"$1$", (2.7, 4), N);
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− | label(scale(0.7)*"$4$", (3.2, 2), E);
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− | </asy>
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− | Now, we easily discover that line <math>CF</math> has lattice coordinates at <math>(1,4)</math> and <math>(3,0)</math>. Hence, the slope of line <math>CF=-2</math>
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− | Plugging in the rest of the coordinate points, we find that line <math>CF=-2x+6</math>
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− | Doing the same process to line <math>BE</math>, we find that line <math>BE=2x</math>.
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− | Hence, setting them equal to find the intersection point...
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− | <math>y=2x=-2x+6\implies 4x=6\implies x=\frac{3}{2}\implies y=3</math>.
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− | Hence, we find that the intersection point is <math>(\frac{3}{2},3)</math>. Call it Z.
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− | Now, we can see that
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− | <math>E=(0,0)</math>
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− | <math>Z=(\dfrac{3}{2},3)</math>
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− | <math>C=(1,4)</math>.
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− | Now use the [[Shoelace Theorem|Shoelace Theorem]].
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− | <math>\frac{(0\cdot 3 + \dfrac{3}{2}\cdot 4 + 1\cdot 0)-(\dfrac{3}{2}\cdot 0 + 1\cdot 3 + 4\cdot 0)}{2} = \frac{6-3}{2} = \frac{3}{2}</math>
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− | Using the [[Shoelace Theorem|Shoelace Theorem]], we find that the area of one of those small shaded triangles is <math>\frac{3}{2}</math>.
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− | Now because there are two of them, we multiple that area by <math>2</math> to get <math>\boxed{\textbf{(C) }3}</math>
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− | ==Solution 4 (Fastest)==
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− | <asy>
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− | draw((0,0)--(3,0)--(3,4)--(0,4)--(0,0)--(2,4)--(3,0));
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− | draw((3,0)--(1,4)--(0,0));
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− | fill((0,0)--(1,4)--(1.5,3)--cycle, black);
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− | fill((3,0)--(2,4)--(1.5,3)--cycle, black);
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− | label("$A$",(3.05,4.2));
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− | label("$B$",(2,4.2));
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− | label("$C$",(1,4.2));
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− | label("$D$",(0,4.2));
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− | label("$E$", (0,-0.2));
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− | label("$F$", (3,-0.2));
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− | label("$G$", (1.5, 3.2), N);
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− | label("$1$", (0.5, 4), N);
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− | label("$1$", (1.5, 4), N);
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− | label("$1$", (2.5, 4), N);
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− | label("$4$", (3.2, 2), E);
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− | </asy>
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− | First, it is easy to see that <math> \triangle CGB \sim \triangle EGF </math>. Therefore, the ratio of the height of <math> \triangle CBG </math> to the height of <math> \triangle EFG </math> is <math> \frac{1}{3} </math>. Thus, the area of <math> \triangle CBG </math> is <math> \frac{1\cdot1}{2} = \frac{1}{2} </math>, and the area of <math> \triangle CBE </math> is <math> \frac{1\cdot4}{2} = 2 </math>. So, the area of <math> \triangle CGE </math> is <math> 2-\frac{1}{2} </math>. Besides, since trapezoid <math> CBEF </math> is isosceles, <math> \triangle CGE \cong \triangle BGF </math>. Hence, the area of the "bat wings" is <math> 2\cdot(2-\frac{1}{2})= \boxed{\textbf{(C) }3} </math>.
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− | ~[[User:Bloggish|Bloggish]]
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| ==Video Solution (CREATIVE THINKING + ANALYSIS!!!)== | | ==Video Solution (CREATIVE THINKING + ANALYSIS!!!)== |
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| ==Video Solutions== | | ==Video Solutions== |
− | *https://youtu.be/Tvm1YeD-Sfg - Happytwin
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| *https://youtu.be/q3MAXwNBkcg ~savannahsolver | | *https://youtu.be/q3MAXwNBkcg ~savannahsolver |
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| https://youtu.be/FDgcLW4frg8?t=4448 ~ pi_is_3.14 | | https://youtu.be/FDgcLW4frg8?t=4448 ~ pi_is_3.14 |
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− | ==Solution 5== | + | ==See Also== |
| + | {{AMC8 box|year=2016|num-b=21|num-a=23}} |
| + | {{MAA Notice}} |