(4/(a^2 - 1)) - (1/(a-1))= (4/(a + 1)(a - 1)) - (1/(a-1))= (4 - (a + 1))/((a+1)(a-1))= (3 - a)/((a+1)(a-1))
(4/(a^2 - 1)) - (1/(a-1))
= (4/(a + 1)(a - 1)) - (1/(a-1))
= (4 - (a + 1))/((a+1)(a-1))
= (3 - a)/((a+1)(a-1))