Update 3_vector_spaces.md

src/3_vector_spaces.md

@@ -222,7 +222,7 @@ Evaluate the following derivatives with respect to the parameter $t$:
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 **4)** [:grinning:] Find the vector product $\vec{b} \times \vec{c}$ and the triple product $\vec{a}\cdot(\vec{b} \times \vec{c})$, where these three vectors are defined as
-$$\vec{a}=\vec{i}+4\vec{j}+\vec{k}\,,$$ and $$\vec{b}=-\vec{i}+2\cos{t}\vec{j}+2\vec{k}\,,$$ and $$\vec{c}=2\vec{i}-\vec{k}\,.$$
+$$\vec{a}=\vec{i}+4\vec{j}+\vec{k}\,,$$ and $$\vec{b}=-\vec{i}+2\vec{j}+2\vec{k}\,,$$ and $$\vec{c}=2\vec{i}-\vec{k}\,.$$
 
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