(z/8 + z/5)*1/z² = (5z/40 + 8z/40)*1/z² = 13z/40*1/z² = 13/40z
==
(a/d - d/a)*4ad/(a + d) = (a² - d²)/ad * 4ad/(a + d) = (a - d)(a + d)/ad * 4ad/(a + d) = 4(a - d)
(z/8 + z/5)*1/z² = (5z/40 + 8z/40)*1/z² = 13z/40*1/z² = 13/40z
==
(a/d - d/a)*4ad/(a + d) = (a² - d²)/ad * 4ad/(a + d) = (a - d)(a + d)/ad * 4ad/(a + d) = 4(a - d)