sin13°cos17°-cos13sin17=1/2 sin140°cos20+sin50sinsin13°cos17°-cos13sin17=1/2sin140°cos20+sin50sin20=√3/2判断那个式子正确
sin13°cos17°-cos13sin17=1/2 sin140°cos20+sin50sinsin13°cos17°-cos13sin17=1/2sin140°cos20+sin50sin20=√3/2判断那个式子正确
sin13°cos17°-cos13sin17=1/2 sin140°cos20+sin50sin
sin13°cos17°-cos13sin17=1/2
sin140°cos20+sin50sin20=√3/2
判断那个式子正确
sin13°cos17°-cos13sin17=1/2 sin140°cos20+sin50sinsin13°cos17°-cos13sin17=1/2sin140°cos20+sin50sin20=√3/2判断那个式子正确
(1)sin13°cos17°-cos13sin17=1/2.不对
因为sin13°cos17°-cos13sin17=sin(13°-17°)=-sin4°≠1/2
(2)sin140°cos20+sin50sin20
=sin40°cos20+sin50sin20
=cos50°cos20+sin50sin20
=cos(50°-20°)
=cos30°
=√3/2.对
下面对,上面错,书上有公式我要详细解答