3·x/(x + 2) + 2·x/(x - 7) = (5·x + 6)/(x + 2)
C.E. (x + 2)·(x - 7) ≠ 0---> x ≠ 7 ∧ x ≠ -2
quindi:
3·x·(x - 7) + 2·x·(x + 2) = (5·x + 6)·(x - 7)
(3·x^2 - 21·x) + (2·x^2 + 4·x) = 5·x^2 - 29·x - 42
5·x^2 - 17·x - (5·x^2 - 29·x - 42) = 0
12·x + 42 = 0--->x = - 7/2