SAT 2 Math Level 2 Graphs : Multiplying

Question

If the graph of f(x) is given,

and the graph of g(x) is given,

How do i identify the graph of f(x).g(x) from the given options?

Answer 1

Pick two points on the graph with the same x-coordinate, multiply their y values together and you'll have the y-coordinate of the product function. Do this for every point and you'll have the new graph. Obviously it's impractical to actually do that for every point so your final graph will be an estimate. For example, if the two y-values are large than the y-value of the product will be proportionately larger. When you're doing this, there are a few rules you should keep in mind:

1. Remember the rules for multiplying positive and negative numbers and think about how that will affect which side of the x-axis the product function is on.
2. Multiplying by a number between -1 and 1 will make the result smaller, not larger.

One quick way to select from multiple choice options is to rely on item (1). You can hopefully eliminate some options just because they're on the wrong side of the x-axis in certain regions.