Let A = {1, 2, 3, 4}. Let R be the equivalence relation on A × A defined by (a, b)R(c, d) if a + d = b + c. Find the equivalence class [(1,3)].
For a 2 × 2 matrix A = [ ], whose elements are given by , write the value of .
If and are unit vectors, then what is the angle between and , so that - is a unit vector ?