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Geometry Difficulty 3.5 AMC 10/12 Find the answer Canada

In the diagram, hexagon PQRSTUPQRSTU has interior right angles at PP, QQ, SS, TT, and UU and an exterior right angle at RR.

Also, PU=UTPU=UT, PQ=ST=10PQ=ST=10, and QS=8QS=8. The perimeter of PQRSTUPQRSTU is closest to

Pick one

Solution

Extend PQPQ and TSTS to meet at point XX.

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Since quadrilateral QRSXQRSX has
three right angles (at QQ, RR and SS), it must have a fourth right angle at
XX.

Thus, QRSXQRSX is a rectangle, which
means that XS=QRXS = QR and QX=RSQX = RS.

The perimeter of PQRSTUPQRSTU is PQ+QR+RS+ST+TU+UP=PQ+XS+QX+ST+TU+UP=(PQ+QX)+(XS+ST)+TU+UP=PX+XT+TU+UP\begin{align*} PQ + QR + RS + ST + TU + UP & = PQ + XS + QX + ST + TU + UP \\ & = (PQ + QX) + (XS + ST) + TU + UP \\ & = PX + XT + TU + UP\end{align*} which is the perimeter
of quadrilateral of PXTUPXTU.

But quadrilateral PXTUPXTU has four
right angles, and so is a rectangle.

Also, PU=UTPU = UT, so PXTUPXTU is a square, and so the perimeter of
PXTUPXTU equals 4×PX=4×(PQ+QX)=4×(10+QX)=40+4×QX4 \times PX = 4\times (PQ + QX) = 4 \times (10 + QX) = 40 + 4 \times QX Finally, $QX
= PX - PQ = PX - 10 = XT - 10 = XT - ST = XS$, which means that
QXS\triangle QXS is isosceles as well
as being right-angled at XX.

By the Pythagorean Theorem, $QX^2 + XS^2 =
QS^2andso and so 2 ×\times QX^2 =
8^2or or QX^2 = 32$.

Since QX>0QX>0, then $QX = 32=16×\sqrt{32} = \sqrt{16 \times} 2} = 16×2=42$.\sqrt{16} \times \sqrt{2} = 4\sqrt{2}\$.

Thus, the perimeter of PQRSTUPQRSTU is
$40 + 4 ×42\times 4\sqrt{2} = 40 + 16216\sqrt{2} \approx 62.6$.

(We could have left this as $40 + 4324\sqrt{32} \approx 62.6$.)

Of the given choices, this is closest to 63.

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Source: CEMC, University of Waterloo, licensed CC-BY-NC-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.