Show that the determinant of the 3x3 matrix (2 1 1 / 2 1 7 / 6 3 5) is equal to zero.

To find the determinant of this matrix, we calculate: 2(1x5-3x7)-1(2x5-6x7)-1(2x3-1x6) = 10 - 42 - 10 + 42 -6 + 6 = 0.So the determinant of this 3x3 matrix is equal to zero.