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2008 MMPC , Part 2 = Michigan Mathematics Prize Competition

p1. Compute (110)12(1102)124(1103)123...\left(\frac{1}{10}\right)^{\frac12}\left(\frac{1}{10^2}\right)^{\frac{1}{2^4}}\left(\frac{1}{10^3}\right)^{\frac{1}{2^3}} ...
p2. Consider the sequence 1,2,2,3,3,3,4,4,4,4,...,1, 2, 2, 3, 3, 3, 4, 4, 4, 4,..., where the positive integer mm appears mm times. Let d(n)d(n) denote the nnth element of this sequence starting with n=1n = 1. Find a closed-form formula for d(n)d(n).
p3. Let 0<θ<π20 < \theta < \frac{\pi}{2}, prove that (sin2θ2+2cos2θ)14+(cos2θ2+2sin2θ)14(68)14 \left( \frac{\sin^2 \theta}{2}+\frac{2}{\cos^2 \theta} \right)^{\frac14}+ \left( \frac{\cos^2 \theta}{2}+\frac{2}{\sin^2 \theta} \right)^{\frac14} \ge (68)^{\frac14} and determine the value of \theta when the inequality holds as equality.
p4. In ABC\vartriangle ABC, parallel lines to ABAB and ACAC are drawn from a point QQ lying on side BCBC. If aa is used to represent the ratio of the area of parallelogram ADQEADQE to the area of the triangle ABC\vartriangle ABC, (i) find the maximum value of aa. (ii) find the ratio BQQC\frac{BQ}{QC} when a=2449.a =\frac{24}{49}. https://cdn.artofproblemsolving.com/attachments/5/8/eaa58df0d55e6e648855425e581a6ba0ad3ea6.png
p5. Prove the following inequality 12009<12345678...20072008<140\frac{1}{2009} < \frac{1}{2} \cdot \frac{3}{4} \cdot \frac{5}{6} \cdot \frac{7}{8}...\frac{2007}{2008}<\frac{1}{40}
PS. You should use hide for answers. Collected [url=https://artofproblemsolving.com/community/c5h2760506p24143309]here.Thanks to gauss202 for sending the problems.