Capacitor Reactance/Impedance Confusion
Some authors specify the reactance of basic circuit elements as an absolute value. Although this is confusing it is not so uncommon. The "trick" is to remember that if you define reactances as:

\[
X_L = \omega L \qquad X_C = \frac{1}{\omega C}
\]

then the impedance for an inductor and a capacitor are:

\[
Z_L = j X_L = j \omega L
\qquad
Z_C = -j X_C = \frac{- j}{\omega C} = \frac {1}{j \omega C}
\]

The problem with this approach is that you must always remember that the reactance as the imaginary part of a generic impedance (i.e. X = Im(z)) is not the same reactance you speak of when talking about "pure" capacitors (there the sign of the reactance is embedded in the value of X).