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5/10

A Strange Operation

An operation &\& on real numbers satisfies, for all reals x,y,zx, y, z,

x&(y&z)=(x&y)+z,x&x=0.x \& (y \& z) = (x \& y) + z, \qquad x \& x = 0.

Compute 2000&20222000 \& 2022.

functionsSubstitutionalgebraFunctional Equations
7/10

Perpendicular Tangents From a Circle

The ellipse Γ:x2a2+y2b2=1\Gamma: \dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1 (a>b>0a > b > 0) has top vertex C(0,1)C(0, 1), and the circle centered at CC with radius 433\dfrac{4\sqrt3}{3} is tangent to …

ExtremaTangent CircleCirclesconic sections+1
7/10

A Quadratic Form Window

Real numbers a,ba, b satisfy

a2ab2b2=1.a^2 - ab - 2b^2 = 1.

Find the range of possible values of a2+b2a^2 + b^2.

SubstitutionalgebraAM-GMinequality
7/10

Two Divisibility Conditions

Find all pairs of positive integers (x,y)(x, y) such that

x+y+12xyandx+y1x2+y21.x + y + 1 \,\mid\, 2xy \qquad\text{and}\qquad x + y - 1 \,\mid\, x^2 + y^2 - 1.
Diophantine Equationsnumber theory
6/10

The Last Interval with an Extremum

The function

f(x)=lnxx+1f(x) = \frac{\ln x}{x + 1}

has an extreme value on the interval [t,+)[t, +\infty), where tNt \in \mathbb{N}^*. Find the maximum possible value of tt.

functionsExtremacalculusMonotonicity+1
6/10

An Angle Bisector Minimum

In triangle ABCABC, the sides opposite angles A,B,CA, B, C are a,b,ca, b, c, and

(a+b)(sinAsinB)=c(sinC+sinB).(a + b)(\sin A - \sin B) = c(\sin C + \sin B).

If the bisector ADAD of angle AA has length 22, fin…

plane geometryLaw of SinestrigonometryLaw of Cosines+2
5/10

A Tangent Rotation Sum

A sequence {xn}\{x_n\} has x1=1x_1 = 1 and

xn+1=3xn+13xn.x_{n+1} = \frac{\sqrt{3}x_n + 1}{\sqrt{3} - x_n}.

Find n=12008xn\displaystyle\sum_{n=1}^{2008} x_n.

trigonometryRecursionsequencesTrigonometric Identities
7/10

A Nested Radical Bound

Prove that

2012+2011++2+1<46.\sqrt{2012 + \sqrt{2011 + \sqrt{\cdots + \sqrt{2 + \sqrt{1}}}}} < 46.
sequencesEstimationInductioninequality
8/10

A Boundary Hunt

Let f(x)=ax2+4x2f(x) = ax^2 + 4x - 2. Suppose the real number aa can be chosen so that

f(x)4for all x[m,0].|f(x)| \leqslant 4 \qquad \text{for all } x \in [m, 0].

Find the minimum possible value of mm, …

functionsQuadratic EquationsAbsolute Valueinequality+1
7/10

A Polarization Range

In the coordinate plane, let A(1,0)A(-1, 0), and let B,CB, C move along the unit circle centered at the origin OO so that the line BCBC has inclination 3030^\circ. Find the range of po…

ExtremaCirclesanalytic geometryvectors
7/10

Common Index Counts

Let {an}\{a_n\} and {bn}\{b_n\} be two distinct infinite sequences, neither constant. Define M={kak=bk, kN}M = \{k \mid a_k = b_k,\ k \in \mathbb{N}^*\}. Determine which of the following statement…

functionsArithmetic ProgressionGeometric ProgressionMonotonicity+1
7/10

A Half-Angle Locus

In the coordinate plane, let A(1,0)A(-1, 0), B(1,0)B(1, 0), and P(x0,y0)P(x_0, y_0), where triangle PABPAB satisfies

tanPAB2=PBAP+AB.\tan\frac{\angle PAB}{2} = \frac{PB}{AP + AB}.

1. Can (0,1)(0, -1) be the …

Law of SinestrigonometryParametrizationanalytic geometry+1

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