How do you find the taylor series series for # (4-x)^(1/2)#?

Answer 1
There's a few different ways this can be done. Probably the most straight-forward approach is to let #f(x)=(4-x)^(1/2)# and write the Taylor series about #x=0# as #f(0)+f'(0)x+(f''(0))/(2!)x^2+(f'''(0))/(3!)x^3+\cdots#
Since #f(x)=(4-x)^(1/2)#, #f(0)=4^{1/2}=2#, #f'(x)=\frac{1}{2}(4-x)^{-1/2}*(-1)#, #f'(0)=-\frac{1}{2}*4^{-1/2}=-\frac{1}{4}#,
#f''(x)=\frac{1}{4}(4-x)^{-3/2}*(-1)#, #f''(0)=-\frac{1}{4}*4^{-3/2}=-\frac{1}{32}#, etc...
Eventually this leads to the Taylor series #2-\frac{1}{4}x-\frac{1}{64}x^2-\frac{1}{512}x^{3}-\cdots#, which converges to #f(x)=(4-x)^{1/2}# for #|x|<4#.
Another approach is to use a bit of slick algebra along with the generalized binomial theorem (discovered by Newton) that #(1+x)^{p}=1+px+\frac{p(p-1}}{2!}x^2+\frac{p(p-1)(p-2)}{3!}x^{3}+\cdots# for #|x|<1#.
We have: #(4-x)^{1/2}=4^{1/2}(1-x/4)^{1/2}=2(1+(-x/4))^{1/2}#. Now use the generalized binomial theorem with #-x/4# in place of #x# and #p=1/2# to get, for #|-x/4|<1 \Leftrightarrow |x|<4#
#(4-x)^{1/2}#
#=2(1+(-x/4))^{1/2}#
#=2(1+(1/2)(-x/4)+\frac{1/2*-1/2}{2!}(-x/4)^2+\frac{1/2*-1/2*-3/2}{3!}(-x/4)^3+\cdots)#
#=2-x/4-\frac{1}{64}x^2-\frac{1}{512}x^{3}-\cdots#
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Answer 2

To find the Taylor series for (4x)1/2(4-x)^{1/2}, follow these steps:

  1. Determine the function and the point about which you want to expand the Taylor series. In this case, the function is (4x)1/2(4-x)^{1/2} and the point is x=0x = 0.
  2. Find the derivatives of the function up to the desired order.
  3. Evaluate the derivatives at the point of expansion (x=0x = 0).
  4. Write out the Taylor series using the formula:

f(x)=f(a)+f(a)(xa)+f(a)2!(xa)2+f(a)3!(xa)3+f(x) = f(a) + f'(a)(x-a) + \frac{{f''(a)}}{{2!}}(x-a)^2 + \frac{{f'''(a)}}{{3!}}(x-a)^3 + \cdots

where f(a)f(a) is the value of the function at the point of expansion and the derivatives are evaluated at that point.

For (4x)1/2(4-x)^{1/2}:

  • f(0)=(40)1/2=2f(0) = (4-0)^{1/2} = 2
  • f(x)=12(4x)1/2f'(x) = -\frac{1}{2}(4-x)^{-1/2}
  • f(x)=14(4x)3/2f''(x) = \frac{1}{4}(4-x)^{-3/2}
  • f(x)=38(4x)5/2f'''(x) = -\frac{3}{8}(4-x)^{-5/2}

Now evaluate these derivatives at x=0x = 0:

  • f(0)=12(40)1/2=14f'(0) = -\frac{1}{2}(4-0)^{-1/2} = -\frac{1}{4}
  • f(0)=14(40)3/2=18f''(0) = \frac{1}{4}(4-0)^{-3/2} = \frac{1}{8}
  • f(0)=38(40)5/2=332f'''(0) = -\frac{3}{8}(4-0)^{-5/2} = -\frac{3}{32}

Plug these values into the Taylor series formula:

(4x)1/2=214x+18x2332x3+(4-x)^{1/2} = 2 - \frac{1}{4}x + \frac{1}{8}x^2 - \frac{3}{32}x^3 + \cdots

This is the Taylor series expansion for (4x)1/2(4-x)^{1/2} centered at x=0x = 0.

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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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