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Problem
Problem
Let
f
f
f
be a function satisfying
2
f
(
x
y
)
=
[
f
(
x
)
]
y
+
[
f
(
y
)
]
x
2f(xy) = [f(x)]^y + [f(y)]^x
2
f
(
x
y
)
=
[
f
(
x
)
]
y
+
[
f
(
y
)
]
x
and
f
(
1
)
=
K
≠
1
f(1) = K \neq 1
f
(
1
)
=
K
=
1
, then
∑
r
=
1
n
f
(
r
)
\sum_{r=1}^n f(r)
∑
r
=
1
n
f
(
r
)
is equal to (a)
K
n
−
1
K^n - 1
K
n
−
1
(b)
K
n
K^n
K
n
(c)
K
n
+
1
K^n + 1
K
n
+
1
(d) none of these
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