Question

Решите систему:
f+d=120
1/f+1/d=1/25

Answer 1

f+d=120 
1/f+1/d=1/25 
f+d/fd=1/25
fd=120*25
f=120-d
120d-d^2=3000
d^2-120d+3000=0
D=14400-12000=2400
d12=(120+-√2400)/2
f12=120-(120+-√2400)/2