化简1+2sin290°•cos430°sin250°+cos790°.
问题描述:
化简
.
1+2sin290°•cos430°
sin250°+cos790°
答
∵sin70°>cos70°,即sin70°-cos70°>0,
∴原式=
=
1−2sin70°cos70°
−sin70°+cos70°
=-
(sin70°−cos70°)2
−sin70°+cos70°
=-1.sin70°−cos70° sin70°−cos70°