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41. For which function is
∑
n
=
0
∞
(
−
1
)
n
x
2
n
(
2
n
)
!
\sum_{n=0}^{\infty} \frac{(-1)^{n} x^{2 n}}{(2 n) !}
∑
n
=
0
∞
(
2
n
)!
(
−
1
)
n
x
2
n
...
Jan 27, 2024
41. For which function is
∑
n
=
0
∞
(
−
1
)
n
x
2
n
(
2
n
)
!
\sum_{n=0}^{\infty} \frac{(-1)^{n} x^{2 n}}{(2 n) !}
∑
n
=
0
∞
(
2
n
)!
(
−
1
)
n
x
2
n
the Taylor series about 0 ? (A)
e
x
e^{x}
e
x
(B)
e
−
x
e^{-x}
e
−
x
(C)
sin
x
\sin x
sin
x
(D)
cos
x
\cos x
cos
x
(E)
ln
(
1
+
x
)
\ln (1+x)
ln
(
1
+
x
)
Generated Graph
Solution by Steps
step 2
This series is recognized as the Taylor series expansion of the cosine function,
cos
(
x
)
\cos(x)
cos
(
x
)
, about 0
step 3
The general form of the Taylor series for
cos
(
x
)
\cos(x)
cos
(
x
)
is
∑
n
=
0
∞
(
−
1
)
n
x
2
n
(
2
n
)
!
\sum_{n=0}^{\infty} \frac{(-1)^{n} x^{2n}}{(2n)!}
∑
n
=
0
∞
(
2
n
)!
(
−
1
)
n
x
2
n
step 4
Therefore, the function for which the given series is the Taylor series about 0 is
cos
(
x
)
\cos(x)
cos
(
x
)
D
Key Concept
Taylor Series of Cosine Function
Explanation
The Taylor series of
cos
(
x
)
\cos(x)
cos
(
x
)
about 0 is
∑
n
=
0
∞
(
−
1
)
n
x
2
n
(
2
n
)
!
\sum_{n=0}^{\infty} \frac{(-1)^{n} x^{2n}}{(2n)!}
∑
n
=
0
∞
(
2
n
)!
(
−
1
)
n
x
2
n
, which matches the given series.
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