cos(4π+a)=?
cos A =1/4\uff0c\u89d2A=?A=arc cos1/4\uff0c\u7ea6\u4e3a75.52249\u5ea6
cosa=\u221a5/5
sina=\u00b12\u221a5/5
\u5f53sina=2\u221a5/5\u65f6
cos(a-\u03c0/4)
= cosacos\u03c0/4+sinasin\u03c0/4
=\u221a5/5*\u221a2/2+2\u221a5/5*\u221a2/2
=\u221a10/10+2\u221a10/10
=3\u221a10/10
\u5f53sina=-2\u221a5/5\u65f6
cos(a-\u03c0/4)
= cosacos\u03c0/4+sinasin\u03c0/4
=\u221a5/5*\u221a2/2-2\u221a5/5*\u221a2/2
=\u221a10/10-2\u221a10/10
=-\u221a10/10
cos a
如果不知道a是神马的话。。那就只能说＝cos a了。。这是神马诱导公式来着。
cosa
cosa
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