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9/10

A Weighted Product Bound

Positive reals a1,,a100a_1, \dots, a_{100} satisfy aia101ia_i \ge a_{101-i} for i=1,,50i = 1, \dots, 50. Define

xk=kak+1a1+a2++ak(k=1,,99).x_k = \frac{k\,a_{k+1}}{a_1 + a_2 + \cdots + a_k} \qquad (k = 1, \dots, 99).

P…

sequencesAM-GMinequality
9/10

Two Zeros and a Power Bound

Let aa be a constant and

f(x)=x(eax+a)+lnx1.f(x) = x\left(e^{ax} + a\right) + \ln x - 1.

1. Discuss the monotonicity of f(x)f(x). 2. Suppose f(x)f(x) has two zeros x1<x2x_1 < x_2.

  1. Find the ran…
functionscalculusSubstitutionMonotonicity+1
9/10

Conservative Sequences

A finite sequence {an}\{a_n\} with k2k \geqslant 2 terms is called conservative if

aiai12for all 2ik.|a_i - a_{i-1}| \leqslant 2 \qquad \text{for all } 2 \leqslant i \leqslant k.

Let TmT_m be …

combinatoricsCountingRecursionsequences+1
9/10

Chebyshev Coefficient Sum

Let f(x)=ax3+bx2+cx+df(x) = ax^3 + bx^2 + cx + d with a0a \neq 0, and suppose f(x)1|f(x)| \leqslant 1 for all x[1,1]x \in [-1, 1]. Find the maximum possible value of

a+b+c+d.|a| + |b| + |c| + |d|.
Absolute ValuealgebraPolynomialsEstimation+1
9/10

A Piecewise Polynomial Ladder

A function f(x)f(x) on (0,+)(0, +\infty) is defined piecewise: for n1<xnn - 1 < x \leqslant n (with nNn \in \mathbb{N}^*),

f(x)=(xn+1)(xn)n.f(x) = (x - n + 1)(x - n)^n.

Determine, with proof, which o…

functionsExtremacalculusEstimation+1
9/10

Reordering a Geometric Sequence

A finite geometric sequence {an}\{a_n\} has NN terms (N3N \geqslant 3), first term a1>0a_1 > 0, and common ratio q(0,1)q \in (0, 1). Its terms are rearranged into a sequence {bn}\{b_n\} suc…

combinatoricsGeometric ProgressionCountingRecursion+1
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