Răspuns :
12 × 8 × ( f - 6) × 89 = 0
12 ×8 × 89 × ( f - 6) = 0
f - 6 = 0 / 12×8×89
f - 6 = 0
f = 6
12 ×8 × 89 × ( f - 6) = 0
f - 6 = 0 / 12×8×89
f - 6 = 0
f = 6