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★ 9/10

Related Numbers of a Set

Let

A2n={1,2,3,…,2n}(n∈N∗, n⩾2).A_{2n} = \{1, 2, 3, \ldots, 2n\} \qquad (n \in \mathbb{N}^*,\ n \geqslant 2).

Call a positive integer mm (m⩾4m \geqslant 4) a related number of A2nA_{2n} if every mm-el…

combinatoricsCountingSet TheoryPigeonhole
★ 8/10

Two Chords, One Fixed Point

Fix the parabola y2=2pxy^2 = 2px and points A(a,b)A(a, b), B(−a,0)B(-a, 0) with ab≠0ab \ne 0 and b2≠2pab^2 \ne 2pa. For a variable point MM on the parabola, the lines AMAM and BMBM meet the parabola…

Parametrizationconic sectionsanalytic geometry
★ 6/10

Three Differences, Ordered

For 0<a<b<π20 < a < b < \dfrac{\pi}{2}, arrange in increasing order:

b−a,sin⁡b−sin⁡a,tan⁡b−tan⁡a.b - a, \qquad \sin b - \sin a, \qquad \tan b - \tan a.
trigonometryMean Value Theoremcalculus
★ 8/10

A Vector-Locked Triangle

In △ABC\triangle ABC, the sides opposite A,B,CA, B, C are a,b,ca, b, c, and

\left|\overrightarrow{BA} + \overrightarrow{BC}\right| = 2, \qquad \overrightarrow{AB}\cdot\overrightarrow{AC…
trigonometryLaw of CosinesCompleting the SquareTriangle Geometry+1
★ 8/10

Four Claims About a Rational Iteration

A sequence {an}\{a_n\} satisfies a1=aa_1=a and

an+1=an2an2−2an+2(n∈N∗).a_{n+1}=\frac{a_n^2}{a_n^2-2a_n+2}\qquad(n\in\mathbb N^{*}).

Determine, with proof, which of the following claims are true.

1. If $a…

MonotonicityRecursionsequencesCasework
★ 7/10

A Wave That Fills Every Window

Let mm be a positive integer and

f(x)=sin⁡(m5x+π3).f(x) = \sin\left(\frac{m}{5}x + \frac{\pi}{3}\right).

Suppose that for every integer nn,

{ f(x)∣n≤x≤n+1 }=[−1,1].…\{\, f(x) \mid n \le x \le n+1 \,\} = [-1, 1]. …
functionstrigonometry
★ 7/10

A Unique Intersection Parameter

Suppose that for x∈[0,1]x\in[0,1], the graphs of y=(mx−1)2y=(mx-1)^2 and y=x+my=\sqrt x+m have exactly one common point. Find the range of the positive real number mm.

functionsConvexityalgebraCasework
★ 8/10

Powers of Sine and Cosine

Let f(x)=sin⁡nx+cos⁡nxf(x) = \sin^n x + \cos^n x, where n∈N∗n \in \mathbb{N}^*.

1. When n=4n = 4, determine whether f(x)f(x) is even, odd, or neither. 2. For even nn, the equation $f(x) = \dfrac{1}{2…

functionstrigonometryExtremaSubstitution+2
★ 8/10

A Tangent Maximum Under Constraints

Given

cos⁡2α+cos⁡2β+cos⁡2γ=1,sin⁡α+sin⁡β+sin⁡γ=0,\cos 2\alpha + \cos 2\beta + \cos 2\gamma = 1, \qquad \sin\alpha + \sin\beta + \sin\gamma = 0,

find the maximum value of tan⁡γ\tan\gamma.

trigonometryExtremaCauchy-Schwarz
★ 7/10

A Unit Jump Equation

Let f(x)=x+1x2+1f(x) = \dfrac{x+1}{x^2+1}. Find the number of real solutions of

∣f(x+1)−f(x)∣=1.\left|f(x+1) - f(x)\right| = 1.
functionsalgebraPolynomialsCasework+1
★ 7/10

A Parallel Secant

The graph of

f(x)=ln⁡xx+1x+xf(x) = \frac{\ln x}{x} + \frac{1}{x} + x

contains three points M,N,PM, N, P with xx-coordinates x1,x2,1x_1, x_2, 1 respectively.

1. Find the equation of the tangent li…

functionscalculusSubstitutionMonotonicity+2
★ 7/10

Three Absolute Values on a Diamond

Find the least real aa such that

∣2x−3y+32∣+∣y−1∣+∣2y−x−3∣≤a\left|2x - 3y + \frac32\right| + |y - 1| + |2y - x - 3| \le a

holds for all x,yx, y with ∣x∣+∣y∣≤1|x| + |y| \le 1.

Linear ProgrammingAbsolute Valuealgebraanalytic geometry+1

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