- Simplify the function
Given
f(x)=22x+1+2x+4+322x+2+16.
Let
Then
So
f(x)=2t2+16t+324t+16=2(t2+8t+16)4(t+4)=2(t+4)24(t+4)=t+42.
Hence
f(x)=2x+42.
- Find a useful symmetry relation
Now compute f(4−x):
f(4−x)=24−x+42.
Since
24−x=2x16,
we get
f(4−x)=2x16+42=16+4⋅2x2⋅2x=2(2x+4)2x.
Therefore
4f(x)=2x+48,
so
f(4−x)=1−4f(x)?
Let us verify directly:
4f(x)+f(4−x)=2x+48+2(2x+4)2x=2(2x+4)16+2x=1.
Thus,
f(4−x)=1−4f(x).
Equivalently,
4f(x)+f(4−x)=1.
- Set up the required sum
We need
8k=1∑59f(15k).
Let
S=k=1∑59f(15k).
Now note that
4−15k=1560−k.
So terms pair as
f(15k)withf(1560−k).
Using the identity,
4f(15k)+f(1560−k)=1.
Also,
4f(1560−k)+f(15k)=1.
Add these two equations:
5[f(15k)+f(1560−k)]=2.
Hence
f(15k)+f(1560−k)=52.
- Count the pairs
The numbers k=1,2,…,59 form pairs
(1,59),(2,58),…,(29,31),
and the middle term is
k=30⟹x=2.
So there are 29 pairs and one unpaired middle term.
Thus
S=29⋅52+f(2).
Now
f(2)=22+42=82=41.
Therefore
S=558+41=20232+5=20237.
- Compute the required value
8S=8⋅20237=5474=94.8.
This is not among the options, so let us instead use the identity more directly in a cleaner way.
From
4f(x)+f(4−x)=1,
for each pair (x,4−x),
4f(x)+f(4−x)=1,
4f(4−x)+f(x)=1.
Subtracting is not useful; adding gave
5(f(x)+f(4−x))=2,
which is correct. So the sum over each pair is indeed 52.
Then
S=29⋅52+41=20237,
and
8S=5474.
Since the answer must be an integer from the options, check whether the intended expression is actually
8(f(151)+f(152)+⋯+f(1559)).
This still gives 94.8.
- Re-check the simplification carefully
Starting again,
f(x)=22x+1+2x+4+322x+2+16.
Let y=2x. Then
f(x)=2y2+16y+324y+16=2(y+4)24(y+4)=y+42,
correct.
Then
f(4−x)=16/y+42=16+4y2y=2(y+4)y.
Hence
f(x)+f(4−x)=y+42+2(y+4)y=2(y+4)4+y=21.
This is the key correct relation.
So actually,
f(x)+f(4−x)=21.
- Now evaluate the sum correctly
Thus each pair satisfies
f(15k)+f(1560−k)=21.
There are 29 such pairs, plus the middle term f(2).
So
S=29⋅21+f(2).
And
f(2)=4+42=41.
Thus
S=229+41=458+1=459.
Therefore
8S=8⋅459=118.
- Compare with options
118 matches Option C.
So the correct answer is C: 118.