Expand (k−2x)12\displaystyle (k - 2x)^{\frac{1}{2}}(k−2x)21 in ascending powers of x x\,x up to and including x3x^3x3, giving your answer in terms of kkk, where k k\,k is a positive constant.
Write down the range of values of x x\,x for which the expansion is valid.
Use your expansion, with a suitable value of xxx, taking k=9k=9k=9, to find the value of 8.9 \sqrt{8.9}\,8.9 correct to 5 significant figures
409 exam-style questions on Edexcel A Level Maths Binomial Expansion, covering 4.1 Expanding (1 + x)^n, 4.2 Expanding (a + bx)^n, and 4.3 Using Partial Fractions. Each one has a worked solution and a mark scheme showing where the marks go.