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Problem of the Week
Problem C and Solution
Cache Circuit

Problem

Maria is setting up a geocaching course. She begins at point \(A\), then walks south \(150\) m to point \(B\), then walks east \(140\) m to point \(C\), and then walks north \(150\) m to point \(D\).

She hides a final cache at point \(E\), which is located \(50\) m east of path \(AB\) and \(30\) m north of path \(BC\), as shown in the diagram.

Determine the distance from \(A\) to \(E\), the distance from \(D\) to \(E\), and the total distance around the five-sided route \(ABCDEA\).

Rectangle ABCD with side AD replaced with a dashed line. Point E is inside the rectangle forming irregular pentagon ABCDE. A dashed line from E, of length 50 m, meets AB at a right angle. A dashed line from E, of length 30 m, meets BC at a right angle.

Note: You may find the following useful:

The Pythagorean Theorem states, "In a right-angled triangle, the square of the length of hypotenuse (the side opposite the right angle) equals the sum of the squares of the lengths of the other two sides."

In the right-angled triangle shown, \(c\) is the hypotenuse, \(a\) and \(b\) are the lengths of the other two sides, and \(c^2=a^2+b^2\).

Solution

Let \(F\) be the point on \(AB\) with \(FE =50\) m. Let \(H\) be the point on \(BC\) with \(EH=30\) m.
Extend \(EF\) to \(G\) on \(CD\).
Since \(ABCD\) is a rectangle and \(FG\) is perpendicular to \(AB\), then \(FG\) is perpendicular to \(CD\) and \(FGCB\) is a rectangle. Therefore, \(FB= EH=GC=30\) m.
Also, \(EG = BC - FE = 140 - 50 = 90\) m, and \(DG = AF = AB - FB = 150 - 30 = 120\) m.

Since \(\triangle AFE\) and \(\triangle DGE\) are right-angled triangles, we can use the Pythagorean Theorem to determine the lengths of \(AE\) and \(DE\).

In \(\triangle AFE\), \(AE^2=AF^2+FE^2 =120^2+50^2 =14\,400+2500 =16\,900\).
Thus, \(AE=130\), since \(AE > 0\).

In \(\triangle DGE\), \(DE^2=DG^2+EG^2 =120^2+90^2 =14\,400+8100 =22\,500\).
Thus, \(DE=150\), since \(DE > 0\).

Therefore, \(AE=130\) m and \(DE=150\) m.
Also, the perimeter of pentagon \(ABCDE\) is equal to \(AB + BC + CD + DE + AE = 150 + 140 + 150 + 150 + 130= 720\) m.