fyqt.net
当前位置:首页 >> sin54°Cos72°=? >>

sin54°Cos72°=?

解: sin54°cos72° =cos36°sin18° =cos36°sin18°cos18°/cos18° =cos36°×1/2sin36°/cos18° =1/4sin72°/cos18° =1/4

cos72°-cos36° =cos(54+18)-cos(54-18) =[cos54cos18-sin54sin18]-[cos54cos18+sin54sin18] =-2sin54sin18 (sin54=cos36) =-2cos36sin18 =-2cos36sin18cos18/cos18 =-cos36sin36/cos18 =-sin72/(2cos18) =-sin72/(2sin72) =-1/2

cos72—cos36 =cos(54+18)-cos(54-18) =[cos54cos18-sin54sin18]-cos54cos18+sin54sin18 =-2sin54sin18 =-2cos36sin18 =-2cos36sin18cos18/cos18 =-cos36sin36/cos18 =-sin72/(2cos18) =-sin72/(2sin72) =-1/2

解答: 利用三倍角公式 sin3a=4sinasin(60°+a)sin(60°-a) 证明如下: sin3a=3sina-4sin^3a =4sina(3/4-sin^2a) =4sina[(√3/2)^2-sin^2a] =4sina(sin^260°-sin^2a) =4sina(sin60°+sina)(sin60°-sina) =4sina*2sin[(60+a)/2]cos[(60°-a)/2]*2sin[(...

sin52=0.7880107536067219 sin53=0.7986355100472928 sin54=0.8090169943749474 ...cos70=0.3420201433256688 cos71=0.32556815445715675 cos72=0.30901699...

cos36-cos72 =cos(54-18)-cos(54+18) =cos54cos18+sin54sin18-[cos54cos18-sin54sin18] =2sin54sin18 =-2sin54sin(-18) =2sin54sin18 =2cos36sin18 =2cos36sin18cos18/cos18 =cos36sin36/cos18 =sin72/(2cos18) =sin72/(2sin72)=1/2

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