wlbk.net
当前位置:首页 >> Cos144 >>

Cos144

-0.81

cos72°+cos144°+cos216°+cos288°=cos72°+cos144°+cos(360°-144°)+cos(360°-72°)=cos72°+cos144°+cos(-144°)+cos(-72°)=cos72°+cos144°+cos144°+cos72°=2(cos72°+cos144°)

cos508°=cos148°,函数y=cosx在(0°,180°)上是减函数,∴cos148°故答案为:

cos144°=cos(90°+54°)=-sin54°则cos24°cos54°-sin24°cos144°=cos24°cos54°+sin24°sin54°由cosacosb+sinasinb=cos(a-b)得原式=cos(54°-24°)=cos30°=√3/2

sin48°cos18°-sin42°cos72°=sin48°cos18°-cos48°sin18°(sina=cos(90°-a))=sin(48°-18°)=sin30°=1/2

cos508=cos148=-sin58=-0.84 cos144=-sin84=-0.81 故cos508<cos144

可以把cos144也化成cos72

cos18*cos36*cos72*cos144上下同乘以16sin18=16*sin18*cos18*cos36*cos72*cos144/(16sin18)反复运用2sinacosa=sin2a=8sin36cos36cos72cos144/(16sin18)=4sin72cos72cos144/(16sin18)=..=sin288/(16sin18)因为:sin(360-a)=-sina=-sin72/(16sin18)=-cos18/(16sin18)=-(1/16)*cot18希望我的回答让你满意

=cos36°+cos72°+cos(180°-72°)+cos(180°-36°)=cos36°+cos72°-cos72°-cos36°=0

①cos508度=cos(360+148)=cos148第二象限的角cos144度;cos508度_②tan(-13派/4)=-tan(3π+π/4)=-tanπ/4tan(-17派/5)=-tan(3π+2π/5)=-tan2π/52π/5>π/4所以tan2π/5>tanπ/4负值相反tan(-13派/4)_>__tan(-17派/5)

hbqpy.net | tfsf.net | 369-e.com | 4405.net | mydy.net | 网站首页 | 网站地图
All rights reserved Powered by www.wlbk.net
copyright ©right 2010-2021。
内容来自网络,如有侵犯请联系客服。zhit325@qq.com