Edexcel Further Pure Maths IGCSE (2017) SAM Paper 2 Q8

Nice 11 mark question on the binomial series.
The method:
- Use the formula for (1+x)^n to find 3(1-2x)^1/2 to the x^3 term
- Let x to -2x to find the values of x for which the expansion is valid and |X| is less than 1
- Use surd manipulation to carry out parts of the question which have few marks and do not require you to use the expansion
- Use the identities discovered earlier in the question to find an approximation for a surd

This question is mainly relevant to
Topic 6 : The Binomial Series

This question is somewhat relevant to
Topic 1 : Logarithms and Indices

[dreamteamvods]

Thank you so much for uploading this! I have a doubt. How did you know you had to substitute root 1-2x for root 0.9 in part e and why did you do that?

[ivashehu]

Hi, just to ask - for 8:06, can every absolute value of x that is negative just be taken as positive? e.g. if in a different question I had |-5x| < 1, would the answer be |x| < 1/5 ? Thank you, and sorry for asking so many questions! Great video :)