(2015²+2013) / (2013²-2015) × (2012²-2012) / (2013×2016-4)
=(2015²+2015-2) / (2013²-2013-2) × [2012×(2012-1) / 2013×(2013+3)-4]
=(2015+2)(2015-1) / (2013+1)(2013-2) × (2012×2011) / (2013²+3×2013-4)
=(2017×2014) / (2014×1011) × (2012×2011) / (2013-1)(2013+4)
=(2017/2011) × (2012×2011 / 2012×2017 )
=(2017/2011)×(2011/2017)
=1