已知cos(π/4+a)=1/3,则cos(3π/4-a)等于几?同题~
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已知cos(π/4+a)=1/3,则cos(3π/4-a)等于几?同题~
已知cos(π/4+a)=1/3,则cos(3π/4-a)等于几?
同题~
已知cos(π/4+a)=1/3,则cos(3π/4-a)等于几?同题~
cos(3π/4-a)=cos(π-π/4-a)
=cos[π-(π/4+a)]
cos(π/4+a)=1/3
cos(3π/4-a)=cos(π-π/4-a)
=cos[π-(π/4+a)]
=-cos(π/4+a)
=-1/3
cos(3π/4-a)=cos(π- π/4-a)=cos[π-(π/4+a)]=-cos(π/4+a)
cos(π/4+a)=1/3
cos(3π/4-a)=-1/3
由cos(π/4+a)=1/3可知cos(-π/4-a)=1/3.........因为cos(-x)=cosx
那么cos(-π/4-a+π)=cos(3π/4-a)=-1/3
貌似是-1/3