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Re: P and Q are two different points on line l
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04 Sep 2026, 10:54
Solution
Since \(PR=QR\), triangle \(PQR\) is isosceles, and the midpoint \(T\) of the base \(PQ\) makes \(RT\) perpendicular to \(PQ\).
So we have a right triangle with:
\(RT=6\)
Let \(PT=TQ=x\). Then:
\(PR=QR=\sqrt{x^2+6^2}=\sqrt{x^2+36}\)
Thus the perimeter is
\(2x+2\sqrt{x^2+36}\)
We need to compare this with 28. Set the perimeter equal to 28:
\(2x+2\sqrt{x^2+36}=28 x+\sqrt{x^2+36}=14\sqrt{x^2+36}=14-x\)
Squaring:
\(x^2+36=196-28x+x^2 28x=160 x=\frac{40}{7}\)
This is possible, so the perimeter can equal 28. But \(P\) and \(Q\) are only specified as different points, so \(x\) is not fixed. The perimeter can be less than, equal to, or greater than 28.
For example:
If \(x=1,\) perimeter \(\approx 14.6<28.\)
If \(x=10\), perimeter \(\approx 48.3>28.\)
Answer: D