f﹙2012﹚
=asin﹙2012π+α﹚+bcos﹙2012π-β﹚
=asinα+bcosβ
=-1
∴f﹙2013﹚
=asin﹙2013π+α﹚+bcos﹙2013π-β﹚
=-asinα-bcosβ
=1