3. Let $L: R^2 \to R^2$ denote the mapping of a vector $\underline{x}$ onto its orthogonal projection on a line $l$ passing through the origin, which forms an angle $\theta$ with the $X$-axis as shown in Figure 2. Let $A$ be the matrix that corresponds to this mapping, i.e., $L(\underline{x}) = A\underline{x}$. Find $A$ by each method below.
(b) (15%)Method 2: Perform a sequential linear transformation \( L(\underline{x}) = L_{\theta} \circ L_{x} \circ L_{-\theta}(\underline{x}) \) as described below: