CH4: As per VBT bonds of CH4 must be non-equivalent.
Co2: electron pairs=2
       bond pairs=2
       non-bond pairs=0
So hybridization is Sp
NH3: sigma bond=3
So hybridization is SP3
There are two carbon oxygen pi bonds in carbon dioxide. these must come from seperate P orbitals.
the remaining p orbital hybredises with the s orbital to form an sp hybrid. this sp hybrid has two lobes which form sigma bonds to o2 molecules on either side of the molecule.

bond angles :if the molecule did not have hybrid orbits and insted had un hybridised p-orbital taking part in the bond formation ,then the bond angle between the orbiottal would be 90 degrees . and as for the real situation the bond angle is nearly 107 wich makes the molecule more stable ,decreasing the bond pair and bond pair lone pair repulsion