The Binomial Series

15 questions

1.11: Show that where and are integers to be found.

4PM1/1/June/2025 — Question 6 · 8 marks

(a) Show that 4x=A(1xB)2\displaystyle \sqrt{4-x} = A\left(1 - \frac{x}{B}\right)^2 where A\displaystyle A and B\displaystyle B are integers to be found.
(2)
(b) Hence expand 4x\displaystyle \sqrt{4-x} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3
Give each coefficient as an exact fraction in its lowest terms.
(3)
(c) Use your expansion with a suitable value of x\displaystyle x to obtain an estimate of 30510\displaystyle \frac{\sqrt{305}}{10}
Give your answer correct to 5 decimal places.
(3)

1.12: Past-paper question 1

4PM1/1/November/2025 — Question 1 · 3 marks

Expand (1x4)2\displaystyle \left(1 - \frac{x}{4}\right)^{-2} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3
Where appropriate, express each coefficient as an exact fraction in its lowest terms.
(3)

1.10: Past-paper question 6

4PM1/1/November/2024 — Question 6 · 12 marks

(a) Show that
a4+bx=a2(1+bx4)12whereaandb are positive integers.\frac{a}{\sqrt{4+bx}} = \frac{a}{2} \left( 1 + \frac{bx}{4} \right)^{-\frac{1}{2}} \mathrm{where} a \mathrm{and} b \text{ are positive integers.}
(2)
The expansion of a4+bx\displaystyle \frac{a}{\sqrt{4+bx}} in ascending powers of x\displaystyle x can be written as
P+Qx+Rx2+Sx3P + Qx + Rx^2 + Sx^3
where P\displaystyle P, Q\displaystyle Q, R\displaystyle R and S\displaystyle S are rational numbers.
(b) Show that Q=ab16\displaystyle Q = -\frac{ab}{16} and S=5ab32048\displaystyle S = -\frac{5ab^3}{2048}
and find P\displaystyle P and R\displaystyle R in terms of a\displaystyle a and b\displaystyle b, as fractions in their lowest terms.
(4)
Given that Q=1285S\displaystyle Q = \frac{128}{5}S and R=9256\displaystyle R = \frac{9}{256}
(c) show that a=3\displaystyle a = 3 and b=1\displaystyle b = 1
(3)
(d) Hence, using an appropriate value of x\displaystyle x, find, to 3 decimal places, an approximate
value for 62\displaystyle \frac{\sqrt{6}}{2}
(3)

1.7: Past-paper question 2

4PM1/1R/June/2024 — Question 2 · 8 marks

Given that
113x+536x2+1 - \frac{1}{3}x + \frac{5}{36}x^2 + \dots
is the binomial expansion, in ascending powers of x\displaystyle x, of (1+Ax)n\displaystyle (1 + Ax)^n
where A\displaystyle A and n\displaystyle n are rational numbers,
(a) find the value of A\displaystyle A and the value of n\displaystyle n
(6)
(b) Hence find the value of the coefficient of x3\displaystyle x^3
Give your answer in the form pq\displaystyle \frac{p}{q} where p\displaystyle p is a prime number and q\displaystyle q is an integer.
(2)

1.8: Past-paper question 7

4PM1/2/June/2024 — Question 7 · 7 marks

(a) Expand (1+2x2)34\displaystyle (1 + 2x^2)^{-\frac{3}{4}} in ascending powers of x\displaystyle x up to and including the term in x6\displaystyle x^6
Express each coefficient as an exact fraction in its lowest terms.
(3)
f(x)=(2+kx)(1+2x2)34wherek0f(x) = \frac{(2 + kx)}{(1 + 2x^2)^{\frac{3}{4}}} \quad \mathrm{where} k \neq 0
(b) Obtain a series expansion for f(x)\displaystyle f(x) in ascending powers of x\displaystyle x up to and including the term in x5\displaystyle x^5
Give each coefficient in terms of k\displaystyle k where appropriate.
(2)
The coefficient of the term in x5\displaystyle x^5 is fourteen times the coefficient of the term in x2\displaystyle x^2
(c) Find the value of k\displaystyle k
(2)

1.9: Past-paper question 2

4PM1/2R/June/2024 — Question 2 · 5 marks

(a) Expand 21+3x\displaystyle \frac{2}{\sqrt{1+3x}} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3
Express each coefficient as a fraction in its simplest terms where appropriate.
(4)
(b) State the range of values of x\displaystyle x for which the expansion is valid.
(1)

1.1: Binomial series and algebraic integration

4PM1/1/June/2022 — Question 5 · 11 marks

Given that (2+3x)1\displaystyle (2+3x)^{-1} can be expressed in the form p(1+qx)1\displaystyle p(1+qx)^{-1}, where p\displaystyle p and q\displaystyle q are constants,
(a) find the value of p\displaystyle p and the value of q\displaystyle q.
(2)
(b) Hence expand (2+3x)1\displaystyle (2+3x)^{-1} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3, expressing each coefficient as an exact fraction in its lowest terms.
(3)
f(x)=1+x2+3x.f(x)=\frac{1+x}{2+3x}.
(c) Obtain a series expansion for f(x)\displaystyle f(x), in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3, expressing each coefficient as an exact fraction in its lowest terms.
(2)
(d) Hence use algebraic integration to obtain an estimate, to 4 decimal places, of
00.5f(x)dx.\int_0^{0.5}f(x)\,\mathrm{d}x.
(4)

1.2: Roots of a quadratic and a new quadratic equation

4PM1/1R/June/2022 — Question 8 · 10 marks

(a) Using the binomial expansion, or otherwise, find the complete expansion of
(x+y)3.(x+y)^3.
(1)
The quadratic equation
2x2+3x+4=02x^2+3x+4=0
has roots α\displaystyle \alpha and β\displaystyle \beta.
(b) Without solving the equation, find the value of
α3+β3.\alpha^3+\beta^3.
(4)
(c) Hence, form a quadratic equation with integer coefficients that has roots
αβ2andβα2.\frac{\alpha}{\beta^2} \qquad \text{and} \qquad \frac{\beta}{\alpha^2}.
(5)

1.3: Binomial expansion and approximation

4PM1/2R/June/2022 — Question 9 · 9 marks

(a) Write
3(3x)3\frac{3}{(3-x)^3}
in the form a(1bx)3\displaystyle a(1-bx)^{-3}, where a\displaystyle a and b\displaystyle b are fractions in their lowest terms.
(2)
(b) Expand 3(3x)3\displaystyle \frac{3}{(3-x)^3} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3. Express each coefficient as a fraction in its lowest terms.
(3)
(c) (i) Use a suitable value of x\displaystyle x with your expansion in part (b), to obtain an approximation for 24125\displaystyle \frac{24}{125} to 5 decimal places.
(ii) Find the percentage error, to 2 decimal places, of your approximation from the actual value.
(4)

1.4: Coefficients in a binomial expansion

4PM1/1/June/2021 — Question 5 · 10 marks

(a) Expand (1+ax)n\displaystyle (1+ax)^n in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3. Express each coefficient of x\displaystyle x in terms of a\displaystyle a and n\displaystyle n, where a\displaystyle a and n\displaystyle n are constants and n>2\displaystyle n>2.
(2)
The coefficient of x\displaystyle x is 15\displaystyle 15 and the coefficient of x2\displaystyle x^2 is equal to the coefficient of x3\displaystyle x^3.
(b) Find the value of a\displaystyle a and the value of n\displaystyle n.
(6)
(c) Find the coefficient of x3\displaystyle x^3.
(2)

1.5: Binomial approximation of square roots

4PM1/1R/November/2020 — Question 5 · 8 marks

(a) Expand 1x\displaystyle \sqrt{1-x} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3. Give each coefficient as an exact fraction in its lowest terms.
(3)
(b) Using your expansion with a suitable value of x\displaystyle x, obtain an approximation, to 6 decimal places, of 0.92\displaystyle \sqrt{0.92}.
(3)
(c) Hence find an approximation, to 5 decimal places, of 23\displaystyle \sqrt{23}.
(2)

1.6: A binomial expansion with related coefficients

4PM1/2/November/2020 — Question 3 · 5 marks

(a) Expand
(1+px)5,p0,(1+px)^{-5}, \qquad p\neq0,
in ascending powers of x\displaystyle x, up to and including the term in x4\displaystyle x^4. Give each term in its simplest form.
(3)
The coefficient of xr\displaystyle x^r in the expansion is cr\displaystyle c_r. Given that
c4=2c3,c_4=2c_3,
(b) find the value of p\displaystyle p.
(2)

1.13: Binomial Series and Approximate Integration

4PM1/1/June/2019 — Question 10 · 14 marks

(a) Expand
(1+2x2)13(1+2x^2)^{-\frac13}
in ascending powers of x\displaystyle x up to and including the term in x6\displaystyle x^6, expressing each coefficient as an exact fraction in its lowest terms.
(3)
(b) State the range of values of x\displaystyle x for which your expansion is valid.
(1)
The function f\displaystyle f is defined by
f(x)=2+kx2(1+2x2)13,k0.f(x)=\frac{2+kx^2}{(1+2x^2)^{\frac13}}, \qquad k\neq0.
(c) Obtain a series expansion for f(x)\displaystyle f(x) in ascending powers of x\displaystyle x up to and including the term in x6\displaystyle x^6.
Give each coefficient in terms of k\displaystyle k where appropriate.
(3)
Given that the coefficient of x4\displaystyle x^4 in the series expansion of f(x)\displaystyle f(x) is zero,
(d) find the value of k\displaystyle k.
(2)
(e) Hence use algebraic integration to obtain an estimate, to 4 decimal places, of
00.5f(x)dx.\int_0^{0.5} f(x)\,\mathrm{d}x.
(5)

1.15: Past-paper question 10

4PM1/1/January/2019 — Question 10 · 11 marks

(a) Expand simplifying each \displaystyle - term in ascending as far as possible. powers of x\displaystyle x up to and including the term in X3,\displaystyle X^{3},
(3)
(b) Write down the range of values of x\displaystyle x for which your expansion is valid.
(1)
f(x)=2x2(12x)\mathrm{f}(x)=\frac{2-x^{2}}{\sqrt{(1-2x)}}
(c) term Find in the series simplifying expansion each of term f(x) in as ascending far as possible. powers of x\displaystyle x up to and including the
(3)
The positive region y-axis is and bounded the line by with the curve equation with equation y=\displaystyle y = f(x), the positive x-axis, the
(d) Using of giving your expansion your answer of f(x) to and decimal algebraic places. integration, find an estimate for the area
(4)

1.14: Binomial Expansion of a Square Root

4PM1/2R/June/2019 — Question 6 · 8 marks

Given that
9x\sqrt{9-x}
can be expressed in the form
p(1+qx)12,p(1+qx)^{\frac12},
where p\displaystyle p and q\displaystyle q are constants,
(a) find the value of p\displaystyle p and the value of q\displaystyle q.
(2)
(b) Hence expand 9x\displaystyle \sqrt{9-x} in ascending powers of x\displaystyle x up to and including the term in x3\displaystyle x^3, expressing each coefficient as an exact fraction in its lowest terms.
(3)
Using the expansion you found in part (b) with a suitable value of x\displaystyle x,
(c) find an estimate to 5 decimal places for the value of
314.\sqrt{\frac{31}{4}}.
(3)