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7/10

A Fixed-Point Transformation

In a sequence {an}\{a_n\}, a1=2a_1 = 2 and

an+1=(21)(an+2),n=1,2,3,a_{n+1} = \left(\sqrt{2} - 1\right)(a_n + 2), \qquad n = 1, 2, 3, \ldots

1. Find a formula for ana_n. 2. A sequence {bn}\{b_n\} has $b_1…

RecursionsequencesInductionTelescoping
8/10

A Differential Inequality

A differentiable function ff on R\mathbb{R} satisfies

(x314)f(2x)2xf(2x)>0for all x.(x - 314)\,f(2x) - 2x\,f'(2x) > 0 \qquad \text{for all } x.

Prove that f(x)<0f(x) < 0 for all xRx \in \mathbb{R}.

calculusMonotonicity
7/10

Two Curves and a Distance

Consider the hyperbola C1:x2y2=1C_1:x^2-y^2=1 and the curve

C2:xy+yx=x2y2.C_2:\frac xy+\frac yx=x^2-y^2.

1. Find the number of intersection points of C1C_1 and C2C_2. 2. Find the minimum distance …

ParametrizationAM-GManalytic geometry
7/10

A Monotone Exp-Log Difference

The function

f(x)=ax1loga(x1)(a>0, a1)f(x) = a^{x-1} - \log_a(x - 1) \qquad (a > 0,\ a \neq 1)

is monotonic on its domain. Find the range of possible values of the real number aa.

functionsExtremacalculusMonotonicity+1
7/10

An Overlap of Congruent Triangles

Points CC and DD lie on the same side of the line ABAB, with ABCBAD\triangle ABC\cong\triangle BAD, AB=9AB=9, BC=AD=10BC=AD=10, and CA=DB=17CA=DB=17. The area of the intersection of the two triang…

plane geometryTriangle GeometrySymmetry
4/10

Sets from Squares

Let A={1,2,m}A = \{1, 2, m\} where mm is a real number. Let B={a2aA}B = \{a^2 \mid a \in A\} and C=ABC = A \cup B. If the sum of all elements of CC is 66, find the product of all elements of $…

Set TheoryalgebraCasework
7/10

A Radical Meets a Line

The graphs of

f(x)=ax2ax+2andg(x)=axa+2f(x) = \sqrt{ax^2 - ax + 2} \qquad\text{and}\qquad g(x) = ax - a + 2

have exactly one common point. Find the range of aa.

functionsalgebraanalytic geometryCasework+1
6/10

A Product Bounded by One-Eighth

Let x,y,z>1x, y, z > 1 with

1x+1y+1z=2.\frac{1}{x} + \frac{1}{y} + \frac{1}{z} = 2.

Prove that

8(x1)(y1)(z1)1.8(x-1)(y-1)(z-1) \leqslant 1.
SubstitutionalgebraAM-GMinequality
8/10

Perpendiculars from the Right Vertex

Let AA be the right vertex of the ellipse E ⁣:x2a2+y2b2=1E \colon \dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1 (with a>b>0a > b > 0). Two mutually perpendicular lines APAP and AQAQ through AA meet th…

ExtremaParametrizationconic sectionsanalytic geometry
5/10

Discrete Subsets

Call a set PP discrete if it has at least 22 elements and the absolute difference of any two of its elements is at least 33. How many subsets of M={1,2,3,,10}M = \{1, 2, 3, \dots, 10\} a…

combinatoricsCounting
7/10

A Forced Shared Root

The inequality

(xm)(x2nx2)0(x - m)(x^2 - nx - 2) \geqslant 0

holds for all x>0x > 0. Find the minimum value of m2+n2m^2 + n^2.

Quadratic EquationsalgebraAM-GMinequality
8/10

Infinitely Many Composites

Prove that there are infinitely many odd positive integers mm for which 8m+9m28^m + 9m^2 is composite.

number theoryModular ArithmeticChinese Remainder Theorem

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