Cho (Δ1):  x12=y13=z1,  (Δ2):  x31=y11=z12\left( {{\Delta _1}} \right):\,\,\dfrac{{x - 1}}{2} = \dfrac{{y - 1}}{3} = \dfrac{z}{1},\,\,\left( {{\Delta _2}} \right):\,\,\dfrac{{x - 3}}{1} = \dfrac{{y - 1}}{1} = \dfrac{{z - 1}}{2}. Khi đó cos(Δ1;Δ2)\cos \angle \left( {{\Delta _1};{\Delta _2}} \right).
A.783\dfrac{7}{{\sqrt {83} }}   
B.784\dfrac{7}{{\sqrt {84} }}   
C.782\dfrac{7}{{\sqrt {82} }}   
D.14\dfrac{1}{4}

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