求帮忙，几题英语的高数题目，谢谢大家！

(un)n∈ℕ is a complex suit such that 2 (un)n and 3 (un)n converge.
Choose one answer.

Then(un) converges
Then(un) diverges
Then(un) converges if the limit of(u2n)n isnot 0
Then(un) converges if the limit of 2 (un)n is 0

English : What is the true and the most accurate assertion ? * (a,b) ∈ ℝ+ × ℝ , we have
Choose one answer.

ab < aln(a)+ exp(b- 1)

ab ≥ aln(a)+ exp(b- 1)

none of the previous answer.
ab ≤ aln(a)+ exp(b- 1)

English : The serie∑ nun with ( )α un = n1∕n - 1
Choose one answer.

converges if and only ifα > 1
converges if and only ifα < 1
never converges
converges for allα ∈ ℝ

English : What is the true and the most accurate assertion ? A function f : ℝ → ℝ derivable which satisfies∀(x,y) ∈ ℝ2,f(x +y) = f(x)+ f(y)
Choose one answer.

can be a polynom of order 2
is affine
is a polynom of order 2
can be affine

English : Considering the functionf(x,y) = x3y2(1+ x - y) fromℝ2 toℝ , the point(- 1, 1) 2 3 is
Choose one answer.

a global maximum
a local maximum
a local minimum
not an extremum

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