How do you find the maclaurin series expansion of #e^(7x)ln((1-x)/3)#?

Answer 1

#f(x) = ln(1/3) + (7ln(1/3) - 1)x + (49ln(1/3) - 15)/(2)x^2 +...#

Note I've left the logs as #ln(1/3)# but could easily rewrite as #-ln(3)#

The maclaurin series is a special case of the Taylor expansion with #x_0 = 0#.

Taylor Expansion:

#f(x) = f(x_0) + (f'(x_0))/(1!)(x-x_0) + (f''(x_0))/(2!)(x-x_0)^2 + (f'''(x_0))/(3!)(x-x_0)^3+...#

So Maclaurin series will be:

#f(x) = f(0) + (f'(0))/(1!)x + (f''(0))/(2!)x^2 + (f'''(0))/(3!)x^3 + ...#
We have #f(x) = e^(7x)ln((1-x)/3)#

I'm only going to compute up to the second derivative, ie quadratic terms of x because this function will just get so messy it'll be easy to make a simple mistake. If you need more either work them out or use one of the various online tools.

Using product rule and chain rule:

#f'(x) = d/(dx)(e^(7x))ln((1-x)/3) + e^(7x)d/(dx)(ln((1-x)/3)))#
#f'(x) = 7e^(7x)ln((1-x)/3) + e^(7x) * (3)/(1-x) * (-1/3)#
#f'(x) = e^(7x)(7ln((1-x)/3) + 1/(x-1))#
#f''(x) = d/(dx)(e^(7x))(7ln((1-x)/3) + 1/(x-1)) + e^(7x)d/(dx)(7ln((1-x)/3) + 1/(x-1)))#
#f''(x) = 7e^(7x)(7ln((1-x)/3) + 1/(x-1)) + e^(7x)(7/(x-1) - 1/(x-1)^2)#
#f''(x) = e^(7x)[49ln((1-x)/3) + 14/(x-1) - 1/(x-1)^2]#
So now that we have these, calculate #f(0), f'(0) and f''(0)#
#f(0) = e^0ln(1/3) = ln(1/3)#
#f'(0) = e^0[7ln(1/3) - 1] = 7ln(1/3) -1#
#f''(0) = e^0[49ln(1/3) - 14 - 1] = 49ln(1/3) - 15#

Hence:

#f(x) = ln(1/3) + (7ln(1/3) - 1)x + (49ln(1/3) - 15)/(2)x^2 +...#
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Answer 2

To find the Maclaurin series expansion of e7xln(1x3)e^{7x} \ln\left(\frac{1-x}{3}\right), we use the formula for the Maclaurin series expansion of a composite function. The formula states that if f(x)f(x) and g(x)g(x) have Maclaurin series expansions, then the Maclaurin series expansion of f(g(x))f(g(x)) is obtained by substituting the series expansion of g(x)g(x) into f(x)f(x), term by term.

Here, f(x)=exf(x) = e^x and g(x)=7xln(1x3)g(x) = 7x \ln\left(\frac{1-x}{3}\right).

The Maclaurin series expansion of exe^x is ex=n=0xnn!e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}.

For g(x)=7xln(1x3)g(x) = 7x \ln\left(\frac{1-x}{3}\right), we need to find its Maclaurin series expansion. We'll use the properties of logarithms and the geometric series to expand ln(1x3)\ln\left(\frac{1-x}{3}\right).

ln(1x3)=ln(1x)ln(3)\ln\left(\frac{1-x}{3}\right) = \ln(1-x) - \ln(3)

=(x+x22+x33+)ln(3)= -\left(x + \frac{x^2}{2} + \frac{x^3}{3} + \ldots\right) - \ln(3)

Now, multiply by 7x7x:

7xln(1x3)=7x27x327x437xln(3)7x \ln\left(\frac{1-x}{3}\right) = -7x^2 - \frac{7x^3}{2} - \frac{7x^4}{3} - \ldots - 7x\ln(3)

Now, substitute this series expansion into the Maclaurin series expansion of e7xe^{7x}:

e7xln(1x3)=e7x(7x27x327x437xln(3))e^{7x} \ln\left(\frac{1-x}{3}\right) = e^{7x}(-7x^2 - \frac{7x^3}{2} - \frac{7x^4}{3} - \ldots - 7x\ln(3))

This gives us the Maclaurin series expansion of e7xln(1x3)e^{7x} \ln\left(\frac{1-x}{3}\right).

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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