cos18°=0.009892对吗
cos18\u5ea6\u662f\u591a\u5c11\u8bbesin18=x,\u5219sin54=sin(90-36)=cos36
\u7531\u4e8e54=18*3,36=18*2\u5229\u7528\u500d\u89d2\u516c\u5f0f
3x-4x^3=1-2x^2
4x^3-2x^2-3x+1=0
(x-1)(4x^2+2x-1)=0
4(x+1/4)^2=5/4
\u6240\u4ee5x=(\u221a5-1)/4
cos18=\u6839\u53f7(1-x^2)=\u221a[2(5+\u221a5)]/4
\u8bbesin18=x,\u5219sin54=sin(90-36)=cos36
\u7531\u4e8e54=18*3,36=18*2\u5229\u7528\u500d\u89d2\u516c\u5f0f
3x-4x^3=1-2x^2
4x^3-2x^2-3x+1=0
(x-1)(4x^2+2x-1)=0
4(x+1/4)^2=5/4
\u6240\u4ee5x=(\u221a5-1)/4
cos18=\u6839\u53f7(1-x^2)=\u221a[2(5+\u221a5)]/4
不对。画个函数图像就看出来了,应该离1很近。
不对
=0.95105616
肯定不对,cos18°>cos60°=1/2
但是0.009892<1/2
cos 余弦!!!!!!!!!初中的定义是:在Rt三角形中,某个锐角的邻边长比上斜边长的值,cos18这个值你可以在计算器上算的。。。。。
还有,照夹逼法你的答案都错的cos18°>cos60°=1/2 但是0.009892<1/2
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