  Two new one-parameter tracking behavior dark energy representations
$\omega=\omega_0/(1+z)$ and $\omega=\omega_0 e^{z/(1+z)}/(1+z)$ are used to
probe the geometry of the Universe and the property of dark energy. The
combined type Ia supernova (SN Ia), Sloan Digital Sky Survey (SDSS), and
Wilkinson Microwave Anisotropy Probe (WMAP) data indicate that the Universe is
almost spatially flat and that dark energy contributes about 72% of the matter
content of the present universe. The observational data also tell us that
$\omega(0)\sim -1$. It is argued that the current observational data can hardly
distinguish different dark energy models to the zeroth order. The transition
redshift when the expansion of the Universe changed from deceleration phase to
acceleration phase is around $z_{\rm T}\sim 0.6$ by using our one-parameter
dark energy models.
