MHB How to Expand the Quantity (t + P)^(1/2) in Terms of t/P?

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The discussion focuses on expanding the expression (t + P)^(1/2) around zero in terms of t/P, yielding four non-zero terms. The series expansion for √(1 + x) is applied, resulting in the approximation √(t + P) = √P{1 + (1/2)(t/P) - (1/8)(t/P)² + (1/16)(t/P)³}. Additionally, a user seeks assistance with evaluating an integral of e^(-4x^4) using its Maclaurin series, specifically asking for the first two non-zero terms to estimate the integral's value accurately. The discussion emphasizes the need for precision in matching the integral's value within a specified tolerance. Overall, the thread highlights mathematical techniques for series expansion and integral approximation.
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Expand the quantity (t + P)^(1/2) about 0 in terms of t/P. Give four non-zero terms.

(t + P)^(1/2) ~
=
 
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ends said:
Expand the quantity (t + P)^(1/2) about 0 in terms of t/P. Give four non-zero terms.

(t + P)^(1/2) ~
=

Applying the series expansion...

$\displaystyle \sqrt{1 + x} = 1 + \frac{1}{2}\ x - \frac{1}{2\ 4}\ x^{2} + \frac{1\ 3}{2\ 4\ 6}\ x^{3} - ...\ (1)$

... You obtain...

$\displaystyle \sqrt{t + P} = \sqrt{P}\ \{1 + \frac{1}{2}\ \frac{t}{P} - \frac{1}{8}\ (\frac{t}{P}^{2}) + \frac{1}{16}\ (\frac{t}{P})^{3} - ...\}\ (2)$

Kind regards

$\chi$ $\sigma$
 
chisigma said:
Applying the series expansion...

$\displaystyle \sqrt{1 + x} = 1 + \frac{1}{2}\ x - \frac{1}{2\ 4}\ x^{2} + \frac{1\ 3}{2\ 4\ 6}\ x^{3} - ...\ (1)$

... You obtain...

$\displaystyle \sqrt{t + P} = \sqrt{P}\ \{1 + \frac{1}{2}\ \frac{t}{P} - \frac{1}{8}\ (\frac{t}{P}^{2}) + \frac{1}{16}\ (\frac{t}{P})^{3} - ...\}\ (2)$

Kind regards

$\chi$ $\sigma$

Thanks a lot! Makes perfect sense. Could you also help me with this one - I have the integral right, but I'm having trouble approximating it perfectly for the online source to consider it correct -

Assume e^x equals it's Maclaurin series for all x. Use the Maclaurin series e^(-4x^4) to evaluate the integral:

*integral sign* from 0 to 0.2 of (e^(-4x^4))dx

Your answer will be an infinite series. Use the first two non-zero terms to estimate it's value, it must match this value to within 10^-7.

Im not sure if I am supposed to enter the decimal approximation, or the series for e^((-4x)^4)
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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