trong>
75°
81°
85°
Correct answer is C
→x.→y=|→x||→y|cosθ
→x.→y=(i−3j).(6i+j)=6−3=3
|→x|=√12+(−3)2=√10
|→y|=√62+12=√37
∴
\cos\theta = \frac{3}{\sqrt{370}} = 0.1559
\theta = \cos^{-1} 0.1559 \approxeq 81°
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