1化简(1)sin负的1071度xsin99度+sin负的171度xsin负的261度(2)1+sin(a-2兀)xsin(兀+a)—2cos平分(—a)1化简(1)sin负的1071度xsin99度+sin负的171度xsin负的261度(2)1+sin(a-2兀)xsin(兀+a)—2cos平分(—a)

Question

1化简 (1)sin负的1071度xsin99度+sin负的171度xsin负的261度(2)1+sin(a-2兀)xsin(兀+a)—2cos平分(—a)
1化简 (1)sin负的1071度xsin99度+sin负的171度xsin负的261度(2)1+sin(a-2兀)xsin(兀+a)—2cos平分(—a) 2求证 (1)sin(360度—a)=—sina(2)cos(360度—a)=cosa(3)tan(360度—a)=—tana

Answer 1

1、
sin(-1071°)sin99°+sin(-171°)sin(-261°)
=sin(-1080°+9°)sin99°-sin(180°-9°)sin(-360°+99°)
=sin9°sin99°-sin9°sin99°
=0
2、
1+sin(α-2π)sin(π+α)-2cos^2(-α)
=1+sinα(-sinα)-2cos^2 α
=1-sin^2 α-2cos^2 α
=cos^2 α-2cos^2 α
=-cos^2 α
3、
sin(360°-α)=sin360°cosα-cos360°sinα
=0*cosα-1*sinα
=-sinα
余下方法相同,省略.