Example

Example: Computing (f⋅g)(x)(f \cdot g)(x) for f(x)=4x−5f(x) = 4x - 5 and g(x)=2x+3g(x) = 2x + 3

Given f(x)=4x−5f(x) = 4x - 5 and g(x)=2x+3g(x) = 2x + 3, this example shows how to find the product function (f⋅g)(x)(f \cdot g)(x) and explains the distinction between function multiplication and function composition.

The notation (f⋅g)(x)(f \cdot g)(x) is different from (f∘g)(x)(f \circ g)(x). In composition, the output of one function is used as the input of another, whereas in multiplication, the two function values are multiplied together.

Using the definition (f⋅g)(x)=f(x)⋅g(x)(f \cdot g)(x) = f(x) \cdot g(x), substitute f(x)=4x−5f(x) = 4x - 5 and g(x)=2x+3g(x) = 2x + 3 to get (f⋅g)(x)=(4x−5)(2x+3)(f \cdot g)(x) = (4x - 5)(2x + 3). Multiply the binomials to obtain (f⋅g)(x)=8x2+2x−15(f \cdot g)(x) = 8x^2 + 2x - 15.

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Updated 2026-06-17

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