Generally, but they tend to go outwards rather than down. i.e. if your tree is, say 40 feet tall, the roots certainly won't go 40 feet down, but may spread 20 feet either side of the tree looking for food & water. The single tap-root does go straight down in order to anchor the tree.

it tends to be the spread of the canopy sideways matches the spread of the roots. so if the daimater of the cannopy is 20ft then the root spread will be similar.

Hardwood trees are often deeper rooted than softwood. I have seen a whole row of conifers 40ft. high blow over in a gale with roots only 5ft. deep.

Root length depends on a number of factors;
Tree type, tree age. Soil composition, terrain. Water availability. Aspect, etc. etc.
For a more definitive answer more imformation is required.