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)