We construct parametric families of (monic) reducible polynomials having two roots very close to each other.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa162-4-6, author = {Yann Bugeaud and Andrej Dujella}, title = {Root separation for reducible integer polynomials}, journal = {Acta Arithmetica}, volume = {166}, year = {2014}, pages = {393-403}, zbl = {1290.11056}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa162-4-6} }
Yann Bugeaud; Andrej Dujella. Root separation for reducible integer polynomials. Acta Arithmetica, Tome 166 (2014) pp. 393-403. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa162-4-6/