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)