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★ 6/10

A Tangent Range from an Inequality

Given that

sin⁡θ3cos⁡θ+1>1,\frac{\sin\theta}{\sqrt 3\cos\theta+1}>1,

find the range of tan⁡θ\tan\theta.

trigonometryTrigonometric IdentitiesCasework
★ 8/10

A Carleman-Style Estimate

Let ai,bi>0a_i, b_i > 0 for 1⩽i⩽n+11 \leqslant i \leqslant n+1, and suppose bi+1−bi⩾δ>0b_{i+1} - b_i \geqslant \delta > 0 for i=1,2,…,ni = 1, 2, \dots, n, where δ\delta is a constant. If $\displaystyle\sum…

algebraAM-GMTelescopinginequality
★ 7/10

Entangled Functions

Functions f(x),g(x)f(x), g(x) on R\mathbb{R} have derivatives f′(x),g′(x)f'(x), g'(x), and

g(x)−f(3−x)=2,f′(x)=g′(x−1),g(−x+2)=−g(x+2).g(x) - f(3 - x) = 2, \qquad f'(x) = g'(x - 1), \qquad g(-x + 2) = -g(x + 2).

Determine, with proof…

functionscalculusFunctional EquationsSymmetry
★ 7/10

A Vector Ratio on a Secant

Consider the circle C:(x−2)2+(y−2)2=1C:(x-2)^2+(y-2)^2=1. Through a point AA on the xx-axis, a line ll meets the circle CC at two points MM and NN with

Power of a Pointanalytic geometry
★ 8/10

An Invariant in a Recursion

Sequences {an}\{a_n\} and {bn}\{b_n\} satisfy a1=1a_1 = 1, b1=2b_1 = 2, and

an+1bn=anbn+2an+4.a_{n+1}b_n = a_nb_n + 2a_n + 4.

1. If additionally bn=2anb_n = 2a_n for all nn, prove that for $n \geqslant …

RecursionsequencesInductionTelescoping+1
★ 7/10

A Necessary Probe

The inequality

3sin⁡2x−cos⁡2x+4acos⁡x+a2≤313\sin^2 x - \cos^2 x + 4a\cos x + a^2 \le 31

holds for all x∈Rx \in \mathbb{R}. Find the range of aa.

Quadratic EquationstrigonometryExtremaSubstitution+1
★ 6/10

A Three-to-One Focal Ratio

Let FF be a focus of the hyperbola C ⁣:x2a2−y2b2=1C \colon \dfrac{x^2}{a^2} - \dfrac{y^2}{b^2} = 1 (with a,b>0a, b > 0). A line through FF is perpendicular to one asymptote, meeting it at AA, a…

Substitutionconic sectionsanalytic geometryvectors
★ 5/10

Three Collinear Roots

The three complex roots of the cubic equation

x3−15x2+kx−1105=0x^3 - 15x^2 + kx - 1105 = 0

correspond to three collinear points in the complex plane. Find the positive integer kk.

complex numbersPolynomialsCaseworkVieta's Formulas
★ 6/10

A Cosine Graph and the Smallest Integer Solution

figure

The figure shows part of the graph of the function f(x)=2cos⁡(ωx+φ)f(x)=2\cos(\omega x+\varphi), where ω>0\omega>0; the graph att…

functionstrigonometryTrigonometric IdentitiesSymmetry
★ 5/10

A Riemann-Style Limit

Evaluate

lim⁡n→+∞∑k=1nn(2n−k)(2n+k).\lim_{n \to +\infty} \sum_{k=1}^{n} \frac{n}{(2n-k)(2n+k)}.
Limitscalculussequences
★ 7/10

An ODE in Disguise

A function f(x)f(x) on (0,+∞)(0, +\infty) has derivative f′(x)f'(x) satisfying

x2f′(x)+xf(x)=ex/2,f(2)=e2.x^2f'(x) + xf(x) = \mathrm{e}^{x/2}, \qquad f(2) = \frac{\mathrm{e}}{2}.

Determine, with proof, which of…

functionsExtremacalculusSubstitution+1
★ 8/10

Extreme Points of a Log-Quadratic

Let f(x)=ln⁡(x+1)+a(x2−x)f(x)=\ln(x+1)+a(x^2-x), where a∈Ra\in\mathbb R.

1. Discuss the number of extreme points of f(x)f(x), with justification. 2. If f(x)⩾0f(x)\geqslant 0 for all x>0x>0, find the range o…

functionsExtremacalculusMonotonicity+1

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