The secret to fixing wide concrete cracks is to undercut the sides of the crack to give it an inverted "V" shape. This helps the repair material to "key" into the crack, creating a mechanical bond in addition to the chemical bond between the patch material and the concrete.
Chisel the crack with a hammer and masonry chisel to widen the base of the crack and to dislodge any loose material from the old concrete.
Remove all debris from the crack, using a wire brush. If desired, clean the crack with a pressure washer or a garden hose and spray nozzle.
Remove all water and debris from the crack with a wet/dry shop vacuum or a brush. Work carefully to remove all dust and grit from the crack. It's OK if the surfaces are wet, but there should be no pools of water.
Mix the concrete patching compound, following the manufacturer's directions.
Trowel the compound into the crack. Stab the trowel into the compound to remove air pockets and help work the patching material deep into the crack. Fill the crack up to the surrounding concrete surface.
Smooth the surface of the patch with the trowel, feathering the compound into the surrounding concrete.
Brush the surface of the patching compound with a dry paintbrush to texture the surface, if desired.
Let the compound cure as directed.
Paint or seal the surface of the patch and surrounding area, if desired.