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MATH / Several figures can be made by attaching two equilateral triangles to the…

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problem

Several figures can be made by attaching two equilateral triangles to the regular pentagon ABCDEABCDE in two of the five positions shown. How many non-congruent figures can be constructed in this way? [asy] pair A,B,C,D,I; A=(10,0); B=(0,0); C=(-3.1,9.5); D=(5,15.4); I=(13.1,9.5); draw(A--B--C--D--I--cycle,linewidth(0.7)); draw(A--B--(5,-8.7)--cycle,dashed); draw(A--I--(19.8,2.1)--cycle,dashed); draw(C--B--(-9.8,2.1)--cycle,dashed); draw(I--D--(14.15,19.4)--cycle,dashed); draw(D--C--(-4.15,19.4)--cycle,dashed); label("AA",A,SE); label("BB",B,SW); label("CC",C,W); label("EE",I,E); label("DD",D,N); [/asy]
Plain-text mathematical notation (without MathML)
Several figures can be made by attaching two equilateral triangles to the regular pentagon ABCDE in two of the five positions shown. How many non-congruent figures can be constructed in this way?

[asy]
pair A,B,C,D,I;
A=(10,0);
B=(0,0);
C=(-3.1,9.5);
D=(5,15.4);
I=(13.1,9.5);
draw(A--B--C--D--I--cycle,linewidth(0.7));
draw(A--B--(5,-8.7)--cycle,dashed);
draw(A--I--(19.8,2.1)--cycle,dashed);
draw(C--B--(-9.8,2.1)--cycle,dashed);
draw(I--D--(14.15,19.4)--cycle,dashed);
draw(D--C--(-4.15,19.4)--cycle,dashed);
label("A",A,SE);
label("B",B,SW);
label("C",C,W);
label("E",I,E);
label("D",D,N);
[/asy]
Original LaTeX notation
Several figures can be made by attaching two equilateral triangles to the regular pentagon $ABCDE$ in two of the five positions shown. How many non-congruent figures can be constructed in this way?

[asy]
pair A,B,C,D,I;
A=(10,0);
B=(0,0);
C=(-3.1,9.5);
D=(5,15.4);
I=(13.1,9.5);
draw(A--B--C--D--I--cycle,linewidth(0.7));
draw(A--B--(5,-8.7)--cycle,dashed);
draw(A--I--(19.8,2.1)--cycle,dashed);
draw(C--B--(-9.8,2.1)--cycle,dashed);
draw(I--D--(14.15,19.4)--cycle,dashed);
draw(D--C--(-4.15,19.4)--cycle,dashed);
label("$A$",A,SE);
label("$B$",B,SW);
label("$C$",C,W);
label("$E$",I,E);
label("$D$",D,N);
[/asy]

level

Level 4

type

Counting & Probability

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