Free thyroxine (free T4) tests are used to help evaluate thyroid function and diagnose thyroid diseases, including hyperthyroidism and hypothyroidism, usually after discovering that the thyroid stimulating hormone (TSH) level is abnormal. T4 and another hormone called triiodothyronine (T3) are produced by the thyroid gland.
[When the determinant of a matrix is nonzero, linear system it represents is linearly independent]. When the determinant of a matrix is zero, it rows are linearly dependent vectors, and its columns are linearly dependent vectors.
About the method. To calculate a determinant you need to do the following steps. 1  Set the matrix (must be square). 2  Reduce this matrix to row echelon form using elementary row operations so that all the elements below diagonal are zero. 3  Multiply the main diagonal elements of the matrix-determinant is calculated.