Which of the following is true for the trace of a 2×22 \times 22×2 matrix A=(abcd)A = \begin{pmatrix} a & b \\ c & d \end{pmatrix}A=(acbd)?
tr(A)=a+b\text{tr}(A) = a + btr(A)=a+b
tr(A)=a+d\text{tr}(A) = a + dtr(A)=a+d
tr(A)=b+c\text{tr}(A) = b + ctr(A)=b+c
tr(A)=a+c\text{tr}(A) = a + ctr(A)=a+c