Final answer:
The operation R2 - 1/2R1 involves replacing the second row of the matrix with the result of subtracting half of the first row from the second row. This is an elementary row operation used in methods like Gaussian elimination.
Step-by-step explanation:
When Yasin performs the elementary row operation represented by R2 - 1/2R1 on matrix A, this involves replacing the second row (R2) of the matrix with the result of the subtraction of half of the first row (1/2 times R1) from the second row (R2). This is a common operation in linear algebra used to manipulate matrices, often for the purposes of solving systems of equations or finding matrix inverses through Gauss-Jordan elimination or Gaussian elimination methods.