Bonjour ,
K = (3/3 + 1/3) : (3/3 - 1/3)
K = 4/3 * 3/2
K = 12/6
K = 2 .
L = [ (a+1)4a^2 / 2a(a-1) ] * (a+1)
L = (a+1)^2 * 4a^2 / 2a (a^2 - 1)
L = (a^2 + 2a + 1) * 4a^2 / 4a^3 - 2a
L = 4a^4 + 8a^3 + 4a^2 / 4a^3 - 2a
L = 4a^4 + 2a^3 + 4a^2 / 2a .
L = 2a (2a^3+a^2+ 2a) / 2a
L = 2a^3 + a^2 + 2a .