ā=(i+2j) b=(2i+2j) c=(2i-4j) c=?

You are looking for the vector \( \mathbf{c} \), which you've provided as \( \mathbf{c} = 2\mathbf{i} - 4\mathbf{j} \).

It seems like you might be asking for additional information or a specific operation involving the vectors \( \mathbf{a} = \mathbf{i} + 2\mathbf{j} \), \( \mathbf{b} = 2\mathbf{i} + 2\mathbf{j} \), and \( \mathbf{c} = 2\mathbf{i} - 4\mathbf{j} \).

Would you like to know how to add them, subtract them, find their dot product, or perform some other operation? Please clarify your question!