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6/10

A Fermat Point in Disguise

Find the minimum value of

f(x,y)=x2+y26y+9+x2+y2+23x+3+x2+y223x+3.f(x, y) = \sqrt{x^2 + y^2 - 6y + 9} + \sqrt{x^2 + y^2 + 2\sqrt{3}x + 3} + \sqrt{x^2 + y^2 - 2\sqrt{3}x + 3}.
plane geometryalgebraanalytic geometryTriangle Geometry+1
6/10

Sum over a Triangular Grid of Arithmetic Progressions

figure

As shown in the figure (which illustrates the case n=4n = 4), an equilateral triangle ABCABC is divided into nn rows…

combinatoricsArithmetic ProgressionsequencesSymmetry
7/10

Two Perpendicular Focal Vectors

The hyperbola C:x2a2y2b2=1C:\dfrac{x^2}{a^2}-\dfrac{y^2}{b^2}=1 (a>0a>0, b>0b>0) has left and right foci F1F_1, F2F_2. A point AA lies on CC and a point BB lies on the yy-axis, with

Law of Cosinesconic sectionsvectors
5/10

Pooled Variance

A class has two math study groups: group AA with 1010 students and group BB with 3030 students. On a test, group AA has mean score 130130 and variance 115115, while group BB has …

Statisticsprobability
6/10

Two Equations, One Sine

Given

π2<βα<π2,sinβ2cosα=1,2sinα+cosβ=2,-\frac{\pi}{2} < \beta - \alpha < \frac{\pi}{2}, \qquad \sin\beta - 2\cos\alpha = 1, \qquad 2\sin\alpha + \cos\beta = \sqrt{2},

find $\sin!\left(\alpha + \dfrac{\pi}{6…

trigonometryTrigonometric Identities
5/10

The Period of a Sine Sum

Find the least positive period of

f(x)=sin2x+sin3x.f(x) = \sin 2x + \sin 3x.
functionstrigonometryTrigonometric Identities
7/10

Counting Zeros with a Parameter

Let a>0a>0 and

f(x)=ln(2x+1)+2ax4aex+4.f(x)=\ln(2x+1)+2ax-4a\mathrm e^x+4.

1. For a=1a=1, find the maximum value of f(x)f(x). 2. Determine the number of zeros of f(x)f(x), and justify your answer.

ExtremacalculusMonotonicityEstimation
7/10

Tangents from the Center

Let P(a,b)P(a, b) be any point on the ellipse x23+y22=1\dfrac{x^2}{3} + \dfrac{y^2}{2} = 1. From the origin OO, two tangent lines to the circle

(xa)2+(yb)2=65(x - a)^2 + (y - b)^2 = \frac{6}{5} \qquad …
Circlesconic sectionsanalytic geometryVieta's Formulas
7/10

Claims About a Line and a Rolling Circle

Consider the circle M:(x+cosθ)2+(ysinθ)2=1M:(x+\cos\theta)^2+(y-\sin\theta)^2=1 and the line l:y=kxl:y=kx. Determine, with proof, which of the following claims are true.

1. For all real kk and θ\theta,…

Tangent CircleCirclesanalytic geometry
8/10

The Largest Shifted Interval

A quadratic function f(x)=ax2+bx+cf(x)=ax^2+bx+c (a,b,cRa,b,c\in\mathbb R, a0a\neq 0) satisfies the following conditions:

1. f(x4)=f(2x)f(x-4)=f(2-x) for all xRx\in\mathbb R, and f(x)xf(x)\geqslant x for al…

functionsQuadratic EquationsExtremaSymmetry
7/10

A Sum Bounded Below

Let f(x)=axlnxf(x) = \dfrac{a}{x} - \ln x with aRa \in \mathbb{R}.

1. Discuss the monotonicity of f(x)f(x). 2. If x1,x2x_1, x_2 are two real solutions of the equation f(x)=2f(x) = 2, prove that

calculusConvexityMonotonicityLogarithms+1
7/10

A Sequence That Grows Like a Root

A sequence satisfies a1=1a_1 = 1 and

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

Prove that a2015>63a_{2015} > 63.

sequencesEstimationTelescopinginequality

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