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★ 6/10

An Exponential Dominates a Log

Let f(x)=ex−2ax−1+2af(x) = \mathrm{e}^x - 2ax - 1 + 2a.

1. For a∈Ra \in \mathbb{R}, discuss the monotonicity of f(x)f(x). 2. Let g(x)=(x−1)ln⁡(x−1)g(x) = (x - 1)\ln(x - 1). If f(x)⩾g(x)f(x) \geqslant g(x) holds for all …

functionsExtremacalculusSubstitution+1
★ 6/10

A Telescoping Log Bound

Let f(x)=x2+(a−2)x−aln⁡xf(x) = x^2 + (a-2)x - a\ln x with a∈Ra \in \mathbb{R}.

1. If a=1a = 1, find the extreme values of f(x)f(x). 2. Discuss the monotonicity of f(x)f(x). 3. For n∈N∗n \in \mathbb{N}^*, p…

ExtremacalculusMonotonicityTelescoping+1
★ 7/10

A Slope-Product Fixed Point

The ellipse E ⁣:x2a2+y2b2=1E \colon \dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1 (with a>b>0a > b > 0) has major axis of length 44, and DD is its right vertex. For any four non-vertex points $P, Q, M…

conic sectionsanalytic geometryVieta's Formulas
★ 7/10

An Absolute-Value Crossing

Let a∈Ra \in \mathbb{R} and

f(x)=∣x2−1∣−x2+ax.f(x) = |x^2 - 1| - x^2 + ax.

1. If f(x)f(x) is even, find aa. 2. Suppose the graph of f(x)f(x) meets the line y=2xy = 2x at exactly 22 points in the f…

functionsQuadratic EquationsAbsolute Valueinequality+1
★ 7/10

A Max Reciprocal Eccentricity Sum

Let F1F_1, F2F_2 be the common foci of an ellipse and a hyperbola, PP a common point of the two, with ∠F1PF2=π3\angle F_1PF_2=\dfrac{\pi}3. Find the maximum value of the sum of the recip…

ExtremaLaw of CosinesCauchy-Schwarzconic sections
★ 8/10

A Quadratic Refinement

If for every acute angle xx,

sin⁡x+tan⁡x−2x>mx2,\sin x + \tan x - 2x > mx^2,

find the range of possible values of the real number mm.

calculusMonotonicityinequality
★ 7/10

A Slope-Two Line Across a Focal-Chord Configuration

figure

As shown in the figure, FF is the focus of the parabola y2=2pxy^2=2px (p>0p>0), and MM is the intersection point of its di…

ParametrizationCompleting the Squareconic sectionsanalytic geometry
★ 5/10

Head and Tail Removed

A sequence {an}\{a_n\} has partial sums SnS_n, with a1=15a_1 = 15 and

(2n−5) an+1=(2n−3) an+4n2−16n+15.(2n-5)\,a_{n+1} = (2n-3)\,a_n + 4n^2 - 16n + 15.

For positive integers m≤nm \le n, find the minimum value of $…

sequences
★ 7/10

A Smallest-Denominator Fraction

A fraction pq\dfrac pq (with p,qp,q positive integers) has decimal expansion pq=0.198…\dfrac pq=0.198\ldots (that is, its decimal begins 0.1980.198). When qq is as small as possible, find $p…

number theoryEstimation
★ 8/10

A Limit Hidden in a Recurrence

A sequence has a1=1a_1 = 1 and

an+1=an+12an.a_{n+1} = a_n + \frac{1}{2a_n}.

Evaluate

lim⁡n→∞(an−n).\lim_{n \to \infty}\left(a_n - \sqrt{n}\right).
LimitscalculussequencesEstimation+1
★ 5/10

Four Powers in Order

Let 0<a<b<1e0 < a < b < \dfrac{1}{\mathrm{e}}. Arrange

aa,bb,ab,baa^a, \quad b^b, \quad a^b, \quad b^a

in increasing order.

functionscalculusMonotonicityalgebra+2
★ 9/10

An Injectivity Condition

Find all complex numbers α\alpha such that for any distinct z1,z2z_1, z_2 with ∣z1∣,∣z2∣<1|z_1|, |z_2| < 1,

(z1+α)2+αz1‾≠(z2+α)…\left(z_1 + \alpha\right)^2 + \alpha\overline{z_1} \ne \left(z_2 + \alpha\right)…
complex numbersAbsolute ValueEstimation

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