c
v
m
v
(
t
x
−
t
)
+
c
k
m
k
(
t
x
−
t
)
=
c
k
m
k
(
t
2
−
t
x
)
c
v
m
v
(
t
x
−
t
)
+
c
k
m
k
(
t
x
−
t
)
=
c
k
m
k
(
t
2
−
t
x
)
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