PSAT Math : How to use FOIL

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : Exponents And The Distributive Property

Factor 2x2 - 5x – 12

Possible Answers:

(x – 4) (2x – 3)

(x - 4) (2x + 3)

(x + 4) (2x + 3)

(x + 4) (2x + 3)

Correct answer:

(x - 4) (2x + 3)

Explanation:

Via the FOIL method, we can attest that x(2x) + x(3) + –4(2x) + –4(3) = 2x2 – 5x – 12.

Example Question #2 : Exponents And The Distributive Property

x > 0.

Quantity A: (x+3)(x-5)(x)

Quantity B: (x-3)(x-1)(x+3)

Possible Answers:

Quantity B is greater

The relationship cannot be determined from the information given

The two quantities are equal

Quantity A is greater

Correct answer:

Quantity B is greater

Explanation:

 

Use FOIL: 

 

  (x+3)(x-5)(x) = (x2 - 5x + 3x - 15)(x) = x3 - 5x2 + 3x2 - 15x = x3 - 2x2 - 15x for A.

 

  (x-3)(x-1)(x+3) = (x-3)(x+3)(x-1) = (x2 + 3x - 3x - 9)(x-1) = (x2 - 9)(x-1)

  (x2 - 9)(x-1) = x3 - x2 - 9x + 9 for B. 

The difference between A and B: 

 (x3 - 2x2 - 15x) - (x3 - x2 - 9x + 9) = x3 - 2x2 - 15x - x3 + x2 + 9x - 9

 = - x2 - 4x - 9. Since all of the terms are negative and x > 0:

  A - B < 0.

Rearrange A - B < 0:

  A < B

 

 

 

Example Question #3 : Exponents And The Distributive Property

Solve for all real values of .

Possible Answers:

Correct answer:

Explanation:

First, move all terms to one side of the equation to set them equal to zero.

All terms contain an , so we can factor it out of the equation.

Now, we can factor the quadratic in parenthesis. We need two numbers that add to and multiply to .

We now have three terms that multiply to equal zero. One of these terms must equal zero in order for the product to be zero.

Our answer will be .

Example Question #1 : How To Use Foil

Simplify: 

Possible Answers:

Correct answer:

Explanation:

In order to simplify this expression, you need to use the FOIL method. First rewrite the expression to look like this: 

Next, multiply your first terms together: 

Then, multiply your outside terms together: 

Then, multiply your inside terms together: 

Lastly, multiply your last terms together: 

Together, you have 

You can combine your like terms, , to give you the final answer: 

Example Question #2 : Exponents And The Distributive Property

Use FOIL to simplify the following product:

Possible Answers:

Correct answer:

Explanation:

Use the FOIL method (first, outside, inside, last) to find the product of:

First:

Outside:

Inside:

Last:

Sum the products to find the polynomial:

Example Question #2 : How To Use Foil

Simplify:

Possible Answers:

Correct answer:

Explanation:

To solve this problem, use the FOIL method. Start by multiplying the First term in each set of parentheses:  

Then multiply the outside terms: 

Next, multiply the inside terms: 

Finally, multiply the last terms: 

When you put the pieces together, you have . Notice that the middle terms cancel each other out, and you are left with . When you distribute the two, you reach the answer: 

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