@article {MATHEDUC.06011784,
    author       = {Unal, Hasan},
    title        = {Proof without words: an arctangent equality.},
    year         = {2011},
    journal      = {Mathematics and Computer Education},
    volume       = {45},
    number       = {3},
    issn         = {0730-8639},
    pages        = {197},
    publisher    = {,},
    msc2010      = {G60xx (E50xx)},
    identifier   = {2012b.00761},
}