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★ 8/10

A Sum of Two Moving Lengths

Plane vectors a,b,c\boldsymbol a,\boldsymbol b,\boldsymbol c satisfy

2∣a∣=∣b∣=2∣c∣=2,a⋅b=1.2|\boldsymbol a|=|\boldsymbol b|=2|\boldsymbol c|=2,\qquad \boldsymbol a\cdot\boldsymbol b=1.

Find the range o…

ExtremaParametrizationvectors
★ 6/10

Trisection Points on a Hypotenuse

Let E,FE, F be the trisection points of the hypotenuse ABAB of an isosceles right triangle ABCABC. Find tan⁡∠ECF\tan\angle ECF.

plane geometrytrigonometryTriangle Geometry
★ 7/10

A Max X Under a Vector Ratio

Let AA and BB be two points on the ellipse x24+y2=m\dfrac{x^2}4+y^2=m (m>1m>1), with P(0,1)P(0,1) and AP→=2PB→\overrightarrow{AP}=2\overrightarrow{PB}. Find the maximum value of the xx-coordinat…

ExtremaSubstitutionconic sections
★ 8/10

A Shifted Crossing Range

Let A(x1,y1)A(x_1, y_1) and B(x2,y2)B(x_2, y_2) be two distinct intersection points of the graphs of

f(x)=ln⁡xxandg(x)=kx2.f(x) = \frac{\ln x}{x} \qquad \text{and} \qquad g(x) = \frac{k}{x^2}.

Find the range …

ExtremacalculusMonotonicitySymmetry
★ 8/10

An Integer Sign Condition

Let f(x)=ax−mf(x) = ax - m (with m∈N∗m \in \mathbb{N}^*) and g(x)=ln⁡xag(x) = \ln\dfrac{x}{a}. If

f(x)⋅g(x)⩾0for every x∈N∗,f(x)\cdot g(x) \geqslant 0 \qquad \text{for every } x \in \mathbb{N}^*,

find the range of pos…

functionsnumber theoryLogarithmsinequality+1
★ 8/10

Extremes as Zeros

Let f(x)=1x−x+2aln⁡xf(x) = \dfrac{1}{x} - x + 2a\ln x, where aa is a real number.

1. If a=12a = \dfrac{1}{2}, find the equation of the tangent line to y=f(x)y = f(x) at (1,f(1))(1, f(1)). 2. Find the inte…

functionsExtremacalculusMonotonicity+1
★ 5/10

Eccentricity from a Minor-Axis Chord

figure

The ellipse x2a2+y2b2=1\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}=1 (a>b>0)(a>b>0) shown has left and right foci F1F_1 and F2F_2. Points AA…

Substitutionconic sectionsanalytic geometry
★ 6/10

K-Points on Conics

Say an ellipse or hyperbola has a KK-point if there is a point PP on it whose distances to the two foci are in ratio 2:12 : 1. Determine, with proof, which of the following curv…

Estimationconic sectionsanalytic geometryCasework
★ 6/10

A Circle Inside an Ellipse with Perpendicular Radii

figure

As shown in the figure, an ellipse is centered at the origin OO with its major axis on the xx-axis and eccentri…

ExtremaCompleting the Squareconic sectionsanalytic geometry
★ 6/10

A Cosine in Disguise

A function ff on R\mathbb{R} satisfies f(1)=14f(1) = \dfrac14 and

4f(x)f(y)=f(x+y)+f(x−y).4f(x)f(y) = f(x+y) + f(x-y).

Find f(2016)f(2016).

functionsRecursionFunctional Equations
★ 5/10

Minimum Area of a Folded Square

figure

A square sheet of paper ABCDABCD with side length 11 is folded so that vertex BB lands at a point B′B' on side ADAD, as show…

plane geometryExtremaReflectionCompleting the Square
★ 8/10

An Acute Cotangent Window

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

b(a+c)sin⁡A=1cos⁡(B+3π2).\frac{b}{(a+c)\sin A} = \frac{1}{\cos\left(B + \dfrac{3\pi}{2}\right)}.

1. Prove that $\cos B = 2…

Law of SinestrigonometryExtremaTrigonometric Identities+1

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