Taylor series of e²ˣ up to degree 4
The Taylor polynomial of degree 4 for e²ˣ about 0 (the Maclaurin polynomial) is 1 + 2x + 2x² + 4x³/3 + 2x⁴/3. The full series converges for every x.
How to work it out
- 1
The Taylor series of f about 0 uses the derivatives of f at 0:
- 2
For f(x) = e²ˣ the first derivatives at 0 are:
- 3
Divide each by k! and keep the terms up to degree 4:
- 4
Radius of convergence: ∞. Inside it, more terms give a better approximation; outside, the series does not settle.
LaTeX source of the formulas on this page
\[ e^{2 x} \approx 1 + 2x + 2x^{2} + \frac{4}{3}x^{3} + \frac{2}{3}x^{4} \]
\[ f(x) = \sum_{k=0}^{\infty} \frac{f^{(k)}(0)}{k!}\,x^k \]
\[ f^{(0)}(0) = 1,\quad f^{(1)}(0) = 2,\quad f^{(2)}(0) = 4,\quad f^{(3)}(0) = 8,\quad f^{(4)}(0) = 16 \]Degree 4 polynomial against the real e²ˣ
| x | Polynomial | Exact | Error |
|---|---|---|---|
| 0.1 | 1.2214000 | 1.2214028 | 2.76e-6 |
| 0.5 | 2.7083333 | 2.7182818 | 9.95e-3 |
| 0.9 | 5.8294000 | 6.0496475 | 2.20e-1 |
| 2 | 34.333333 | 54.598150 | 2.03e+1 |
Questions
What is the Taylor series of e²ˣ?
1 + 2x + 2x² + 4x³/3 + 2x⁴/3 + 4x⁵/15 + 4x⁶/45 + 8x⁷/315 + 2x⁸/315 + …
What is the degree 4 Taylor polynomial of e²ˣ?
1 + 2x + 2x² + 4x³/3 + 2x⁴/3
What is the radius of convergence of the series of e²ˣ?
∞
What is the Maclaurin series?
A Taylor series centred at 0.