a) \( \lim{ (-1)^n \frac{2n^2+1}{n^2+n} } = ? \)
b) \( \lim{ (-1)^n \frac{2n+1}{n^2+n} } = ? \)
c) \( \lim{ (-1)^n \frac{2n^2+1}{n+1} } = ? \)
d) \( \lim{ (-1)^n \frac{2n^3+9}{n^3+1} } = ? \)
e) \( \lim{ \frac{(-5)^n+4}{5^n+6} } = ? \)
f) \( \lim{ \left( \frac{2n-n^2}{3n+n^2} \right)^n } = ? \)