If you are given f(x) and you are asked to graph y=2(f(x)):
Note that the type of graph will not change. So a line remains a line, a parabola remains a parabola, etc... Multiplying by 2 is a dilation (stretch) of factor 2.
You can build a table with the following headings: x ; f(x) ; 2f(x) and plot the points.
Alternatively, you can graph y=f(x) and then take each y-value and double it to form the graph of y=2f(x).
For example, if `y=x^2` then you have, among others, the points (-2,4),(-1,1),(0,0),(1,1),(2,4). The function `y=2f(x)=2x^2` has the following points: (-2,8),(-1,2),(0,0),(1,2),(2,8)