已知sin(a-π/4)=1/3,则cos(a+π/4)=?
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已知sin(a-π/4)=1/3,则cos(a+π/4)=?
已知sin(a-π/4)=1/3,则cos(a+π/4)=?
已知sin(a-π/4)=1/3,则cos(a+π/4)=?
cos(a+π/4) = cos(π/2-(π/4-a)) = sin(π/4-a) = -sin(a-π/4) = -1/3
根据sinα=-sin(α+1/2π)得到sin(a-π/4)=-sin(a-π/4+1/2π)=-sin(a+π/4)=1/3
则sin(a+π/4)=-1/3
所以cos(a+π/4)=±√(1-sin(a+π/4)²)=±2/3√2
cos(a+π/4) = cos(a-π/4+π/2)=-sin(a-π/4)=-1/3