在$△ABC$中, 已知向量$\overrightarrow{AB}=\left(COS{18}^{\mathrm{°}},COS{72}^{\mathrm{°}}\right)$, $\overrightarrow{AC}=\left(2\cos {63}^{\mathrm{°}},2\cos {27}^{\mathrm{°}}\right)$,则$\cos \angle BAC$的值为(   )

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     A dog is walking along a road. It is a big dog. It is carrying a piece of meat. The piece of meat is in the dog's mouth. The dog is walking across a bridge now.There is water under the bridge. The water is very deep. The dog is looking into the water. It can see a dog in the water. This dog has a piece of meat in its mouth, too. The big dog is barking at the dog in the water. It wants its piece of meat, too. The big dog's piece of meat is falling into the water.