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A) Find the binomial expansion of sqrt(1-8x), |x| < (1)/(8), in ascending powers of x up to and including the term in x3, simplifying each term. b) Show that, when x = (1)/(100), the exact value of sq

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3 parts
b
Shown:

, when x=1100x = \frac{1}{100}, the exact value of 1−8x\sqrt{1-8x} is 235\frac{\sqrt{23}}{5}

c
4.79584
d

A=64,B=160,C=20A=64, B=160, C=20

Step-by-step solution

10 steps

here are the solutions to question 2.

2. a) Find the binomial expansion of 1−8x\sqrt{1-8x}, ∣x∣<18|x| < \frac{1}{8}, in ascending powers of xx up to and including the term in x3x^3, simplifying each term.

Step 1: Rewrite the expression in the form (1+y)n(1+y)^n.

1−8x=(1−8x)12\sqrt{1-8x} = (1-8x)^{\frac{1}{2}}

Here, n=12n = \frac{1}{2} and y=−8xy = -8x.

Step 2: Apply the binomial expansion formula (1+y)n=1+ny+n(n−1)2!y2+n(n−1)(n−2)3!y3+…(1+y)^n = 1 + ny + \frac{n(n-1)}{2!}y^2 + \frac{n(n-1)(n-2)}{3!}y^3 + \dots.

(1−8x)12=1+(12)(−8x)+12(12−1)2!(−8x)2+12(12−1)(12−2)3!(−8x)3+…(1-8x)^{\frac{1}{2}} = 1 + \left(\frac{1}{2}\right)(-8x) + \frac{\frac{1}{2}\left(\frac{1}{2}-1\right)}{2!}(-8x)^2 + \frac{\frac{1}{2}\left(\frac{1}{2}-1\right)\left(\frac{1}{2}-2\right)}{3!}(-8x)^3 + \dots

Step 3: Simplify each term.

=1+(12)(−8x)+12(−12)2(64x2)+12(−12)(−32)6(−512x3)+…= 1 + \left(\frac{1}{2}\right)(-8x) + \frac{\frac{1}{2}\left(-\frac{1}{2}\right)}{2}(64x^2) + \frac{\frac{1}{2}\left(-\frac{1}{2}\right)\left(-\frac{3}{2}\right)}{6}(-512x^3) + \dots =1−4x+−142(64x2)+386(−512x3)+…= 1 - 4x + \frac{-\frac{1}{4}}{2}(64x^2) + \frac{\frac{3}{8}}{6}(-512x^3) + \dots =1−4x−18(64x2)+348(−512x3)+…= 1 - 4x - \frac{1}{8}(64x^2) + \frac{3}{48}(-512x^3) + \dots =1−4x−8x2−32x3+…= 1 - 4x - 8x^2 - 32x^3 + \dots

The binomial expansion is 1−4x−8x2−32x3\boxed{1 - 4x - 8x^2 - 32x^3}.

Part b· 2 steps

Show that, when x=1100x = \frac{1}{100}, the exact value of 1−8x\sqrt{1-8x} is 235\frac{\sqrt{23}}{5}.

  1. Substitute x=1100x = \frac{1}{100} into the expression 1−8x\sqrt{1-8x}.

    1−8(1100)\sqrt{1 - 8\left(\frac{1}{100}\right)}
  2. Simplify the expression.

    =1−8100= \sqrt{1 - \frac{8}{100}} =1−225= \sqrt{1 - \frac{2}{25}} =2525−225= \sqrt{\frac{25}{25} - \frac{2}{25}} =2325= \sqrt{\frac{23}{25}} =2325= \frac{\sqrt{23}}{\sqrt{25}} =235= \frac{\sqrt{23}}{5}

    This shows that the exact value of 1−8x\sqrt{1-8x} is 235\boxed{\frac{\sqrt{23}}{5}}.

Part c4.79584

Substitute x=1100x = \frac{1}{100} into the expansion in part (a) and hence obtain an approximation to 23\sqrt{23}. Give your answer to 5 decimal places.

  1. Substitute x=1100=0.01x = \frac{1}{100} = 0.01 into the expansion from part (a)

    1−4x−8x2−32x31 - 4x - 8x^2 - 32x^3.

    1−8x≈1−4(0.01)−8(0.01)2−32(0.01)3\sqrt{1-8x} \approx 1 - 4(0.01) - 8(0.01)^2 - 32(0.01)^3
  2. Calculate the value.

    =1−0.04−8(0.0001)−32(0.000001)= 1 - 0.04 - 8(0.0001) - 32(0.000001) =1−0.04−0.0008−0.000032= 1 - 0.04 - 0.0008 - 0.000032 =0.96−0.0008−0.000032= 0.96 - 0.0008 - 0.000032 =0.9592−0.000032= 0.9592 - 0.000032 =0.959168= 0.959168
  3. Use the result from part (b) to find an approximation for 23\sqrt{23}.

    We know 235≈0.959168\frac{\sqrt{23}}{5} \approx 0.959168.

    23≈5×0.959168\sqrt{23} \approx 5 \times 0.959168 23≈4.79584\sqrt{23} \approx 4.79584
  4. Round the answer to 5 decimal places.

    23≈4.79584\sqrt{23} \approx 4.79584

    The approximation to 23\sqrt{23} is 4.79584\boxed{4.79584}.

Part d

A=64,B=160,C=20A=64, B=160, C=20

Given that (2+x)5+(2−x)5=A+Bx2+Cx4(2+x)^5 + (2-x)^5 = A + Bx^2 + Cx^4, find the constants AA, BB and CC.

  1. Expand (2+x)5(2+x)^5 using the binomial theorem (a+b)n=∑k=0n(nk)an−kbk(a+b)^n = \sum_{k=0}^n \binom{n}{k} a^{n-k} b^k.

    (2+x)5=(50)25x0+(51)24x1+(52)23x2+(53)22x3+(54)21x4+(55)20x5(2+x)^5 = \binom{5}{0}2^5x^0 + \binom{5}{1}2^4x^1 + \binom{5}{2}2^3x^2 + \binom{5}{3}2^2x^3 + \binom{5}{4}2^1x^4 + \binom{5}{5}2^0x^5 =1(32)(1)+5(16)x+10(8)x2+10(4)x3+5(2)x4+1(1)x5= 1(32)(1) + 5(16)x + 10(8)x^2 + 10(4)x^3 + 5(2)x^4 + 1(1)x^5 =32+80x+80x2+40x3+10x4+x5= 32 + 80x + 80x^2 + 40x^3 + 10x^4 + x^5
  2. Expand (2−x)5(2-x)^5.

    This is similar to (2+x)5(2+x)^5, but with alternating signs for odd powers of xx.

    (2−x)5=(50)25(−x)0+(51)24(−x)1+(52)23(−x)2+(53)22(−x)3+(54)21(−x)4+(55)20(−x)5(2-x)^5 = \binom{5}{0}2^5(-x)^0 + \binom{5}{1}2^4(-x)^1 + \binom{5}{2}2^3(-x)^2 + \binom{5}{3}2^2(-x)^3 + \binom{5}{4}2^1(-x)^4 + \binom{5}{5}2^0(-x)^5 =1(32)(1)+5(16)(−x)+10(8)x2+10(4)(−x3)+5(2)x4+1(1)(−x5)= 1(32)(1) + 5(16)(-x) + 10(8)x^2 + 10(4)(-x^3) + 5(2)x^4 + 1(1)(-x^5) =32−80x+80x2−40x3+10x4−x5= 32 - 80x + 80x^2 - 40x^3 + 10x^4 - x^5
  3. Add the two expansions.

    (2+x)5+(2−x)5=(32+80x+80x2+40x3+10x4+x5)+(32−80x+80x2−40x3+10x4−x5)(2+x)^5 + (2-x)^5 = (32 + 80x + 80x^2 + 40x^3 + 10x^4 + x^5) + (32 - 80x + 80x^2 - 40x^3 + 10x^4 - x^5)

    Combine like terms:

    =(32+32)+(80x−80x)+(80x2+80x2)+(40x3−40x3)+(10x4+10x4)+(x5−x5)= (32+32) + (80x-80x) + (80x^2+80x^2) + (40x^3-40x^3) + (10x^4+10x^4) + (x^5-x^5) =64+0x+160x2+0x3+20x4+0x5= 64 + 0x + 160x^2 + 0x^3 + 20x^4 + 0x^5 =64+160x2+20x4= 64 + 160x^2 + 20x^4
  4. Compare this result with A+Bx2+Cx4A + Bx^2 + Cx^4.

    By comparing the coefficients:
    A=64A = 64
    B=160B = 160
    C=20C = 20
    The constants are A=64,B=160,C=20\boxed{A=64, B=160, C=20}.

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