Cách làm cho bạn:
Ta có:
$\widehat{xOM} = 135^{o}$
=>$ sin\widehat{xOM} = \frac{\sqrt{2}}{2}$
=> $cos\widehat{xOM} = -\frac{\sqrt{2}}{2}$
$x_{M}.y_{M} = \frac{\sqrt{2}}{2} . (-\frac{\sqrt{2}}{2}) = -\frac{1}{2}$
=> Đáp án B
$C. \frac{-1}{2}$.
$D. A. -\frac{1}{2\sqrt{2}}$.
Ta có:
$\widehat{xOM} = 135^{o}$
=>$ sin\widehat{xOM} = \frac{\sqrt{2}}{2}$
=> $cos\widehat{xOM} = -\frac{\sqrt{2}}{2}$
$x_{M}.y_{M} = \frac{\sqrt{2}}{2} . (-\frac{\sqrt{2}}{2}) = -\frac{1}{2}$
=> Đáp án B
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