Hence, all the three
will have negative signs Thus,
B¢ P = –v, FP = –f, BP = –u
Using these in Eq (9 6), we get
–
–
v–
f
v
f
u
+
= –
or
v–
f
v
f
u
=
      v
f
uv
=
+
1
Dividing it by v, we get
      
1
1
1
v
u
f
+
=
(9