1. The problem asks to find an expression equivalent to the vector \( \left( \begin{array}{l} r \\ t \end{array} \right) \).\n\n2. This vector represents a point or direction in 2D space with components \(r\) and \(t\).\n\n3. To find an equivalent expression, we consider operations like scalar multiplication, addition, or rewriting in terms of other vectors or components.\n\n4. Without additional context or options, the vector itself is the simplest form. Any equivalent expression must preserve the components \(r\) and \(t\).\n\n5. For example, if \(r\) and \(t\) are variables, the vector can be expressed as \(r\mathbf{i} + t\mathbf{j}\), where \(\mathbf{i} = \left( \begin{array}{l} 1 \\ 0 \end{array} \right)\) and \(\mathbf{j} = \left( \begin{array}{l} 0 \\ 1 \end{array} \right)\).\n\n6. Therefore, an equivalent expression is \n$$\left( \begin{array}{l} r \\ t \end{array} \right) = r\left( \begin{array}{l} 1 \\ 0 \end{array} \right) + t\left( \begin{array}{l} 0 \\ 1 \end{array} \right) = r\mathbf{i} + t\mathbf{j}$$\n\nThis shows the vector as a linear combination of the standard basis vectors in 2D space.