What's the coefficient of x^2 in the expansion of (2 - 1/2x)^4

(I've no idea hw to go bout this & I would also like to know under which topic it falls)

1 answer

It falls under the binomial theorem or binomial expansion when there are finite terms (this case).
When the number of terms is infinite, such as
(2-x/2)^(-3), then it falls under Taylor's series.
Following are some typical references:
http://mathworld.wolfram.com/BinomialSeries.html
http://www.purplemath.com/modules/binomial.htm
http://tutorial.math.lamar.edu/Classes/CalcII/TaylorSeries.aspx