Question 253003
( 1/a + a )^2 = (1/a)2+a^2+2*(1/a)*a
(1/a + a )^2  = (1/a)2+a^2+2   ...(1)
Next,
( 1/a – a )^2 = (1/a)2+a^2-2*(1/a)*a
( 1/a – a )^2 = (1/a)2+a^2-2   ...(2)
(1)-(2) =>
( 1/a + a )^2  - ( 1/a – a )^2 = [(1/a)2+a^2+2]-[(1/a)2+a^2-2]
                               = (1/a)2+a^2+2-(1/a)2-a^2+2
                               = 4