4 - (1 / 2a) = (7 / 2) - a
(8a / 2a) - (1 / 2a) = (7a / 2a) - (2a^2 / 2a)
(8a - 1) / 2a = (7a - 2a^2) / 2a
8a - 1 = 7a - 2a^2
2a^2 + 8a - 7a - 1 = 0
2a^2 + a - 1 = 0
2a^2 + 2a - a - 1 = 0
(2a^2 + 2a) - (a + 1) = 0
(2a)(a + 1) - (1)(a + 1) = 0
(2a - 1)(a + 1) = 0
2a - 1 = 0 or a + 1 = 0
a = 1/2 or a = -1