If a function f(x) contains no frequencies higher than f hertz, it is completely determined by giving its ordinates at a series of points spaced 1/2f seconds apart.
A sufficient sample-rate is therefore anything larger than 2f samples per second. Equivalently, for a given sample rate fs, perfect reconstruction is guaranteed possible for a bandlimit N<fs/2
PEMDAS states that the value in the parenthesis should be evaluated first: 4(5*6) 4(30) After just multiply the value in the parenthesis by the number outside of the parenthesis: 120
