If a(x) and b(x) are linear functions with one variable, which of the following expressions produces a quadratic function? (ab)(x) (a – b)(x) (a + b)(x)

For this case we have that by definition, a linear function is of the form

If we have that a and b are linear functions, then they are of the form:

If we multiply them we have: (Applying distributive property)

That is, we get a quadratic function.