sin71°cos64°＋sin19°sin64°
=cos19°cos64°＋sin19°sin64°
=cos(19°－64°)
=cos(－45°)
=cos45°
=√2/2已知tanα＝4，tanβ＝3,则tan﹙α＋β﹚等于tan(a＋b)=[tana＋tanb]/[1－tanatanb]=－7/11