- Simplify the product
We use the identity
(1−x)(1+x)(1+x2)(1+x4)(1+x8)(1+x16)=1−x32.
Hence,
(1+x)(1+x2)(1+x4)(1+x8)(1+x16)=1−x1−x32,x=1.
So
y(x)=1−x1−x32=1+x+x2+⋯+x31.
This polynomial form is valid for all x, so we can differentiate termwise.
- Differentiate
Since
y(x)=k=0∑31xk,
we get
y′(x)=k=1∑31kxk−1,
and
y′′(x)=k=2∑31k(k−1)xk−2.
We need y′(−1)−y′′(−1).
- Compute y′(−1)
y′(−1)=k=1∑31k(−1)k−1.
This is the alternating sum
1−2+3−4+⋯+31.
Pair terms:
(1−2)+(3−4)+⋯+(29−30)+31.
There are 15 pairs, each equal to −1, so
y′(−1)=15(−1)+31=16.
- Compute y′′(−1)
y′′(−1)=k=2∑31k(k−1)(−1)k−2.
Since (−1)k−2=(−1)k, this becomes
y′′(−1)=k=2∑31k(k−1)(−1)k.
Write terms in pairs:
(2⋅1)−(3⋅2)+(4⋅3)−(5⋅4)+⋯+(30⋅29)−(31⋅30).
Now pair as
(2⋅1−3⋅2)+(4⋅3−5⋅4)+⋯+(30⋅29−31⋅30).
For a general pair with even k=2m:
(2m)(2m−1)−(2m+1)(2m)=2m[(2m−1)−(2m+1)]=−4m.
Here m=1,2,…,15. Therefore
y′′(−1)=m=1∑15(−4m)=−4⋅215⋅16=−480.
- Compute the required value
y′(−1)−y′′(−1)=16−(−480)=496.
- Compare with the stored answer
Derived answer is 496, which matches Option A.