P
1
=
ρ
V
g
−
ρ
1
V
g
=
(
ρ
−
ρ
1
)
⋅
V
g
P
1
=
ρ
V
g
−
ρ
1
V
g
=
(
ρ
−
ρ
1
)
⋅
V
g