3/(x - 4) - 21/(x + 2) = 3/4 - 21/4
3/(x - 4) - 21/(x + 2) = - 18/4 | ·4·(x - 4)·(x + 2)
3·4·(x + 2) - 21·4·(x - 4) = - 18·(x - 4)·(x + 2)
12·x + 24 - 84·x + 336 = - 18·x^2 + 36·x + 144
18·x^2 - 108·x + 216 = 0
x^2 - 6·x + 12 = 0
Hier gibt es keine Lösung :(