PSAT Math : How to use FOIL in the distributive property

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #11 : How To Use Foil In The Distributive Property

If \(\displaystyle f(x) = 3x-2\)\(\displaystyle g(x) = 2x+3\), and \(\displaystyle h(x) = f(x) \times g(x)\), then \(\displaystyle h(x) =?\)

Possible Answers:

\(\displaystyle 6x-1\)

\(\displaystyle 6x^{2}-4x-6\)

\(\displaystyle 6x^{2} + 9x +6\)

\(\displaystyle 6x-6\)

\(\displaystyle 6x^{2} +5x-6\)

Correct answer:

\(\displaystyle 6x^{2} +5x-6\)

Explanation:

To find what \(\displaystyle h(x)\) equals, you must know how to multiply \(\displaystyle f(x)\) times \(\displaystyle g(x)\), or, you must know how to multiply binomials. The best way to multiply monomials is the FOIL (first, outside, inside, last) method, as shown below:

\(\displaystyle h(x) = f(x)\times g(x) = (3x-2)\times (2x+3)\)

Multiply the First terms

\(\displaystyle 3x\cdot 2x= 6x^{2}\)

Multiply the Outside terms:

\(\displaystyle 3x\cdot3 = 9x\)

Multiply the Inside terms:

\(\displaystyle -2\cdot2x = -4x\)

Note: this step yields a negative number because the product of the two terms is negative.

Multiply the Last terms:

\(\displaystyle -2\cdot3=-6\)

Note: this step yields a negative number too!

Putting the results together, you get:

\(\displaystyle (3x-2)\times (2x+3) = 6x^{2} +9x-4x -6\)

Finally, combine like terms, and you get:

\(\displaystyle h(x) = 6x^{2} +5x-6\)

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