ACT Math : How to use FOIL with exponents

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : Exponents And The Distributive Property

For all x,\ (5x+2)^{2}=\(\displaystyle x,\ (5x+2)^{2}=\) ?

Possible Answers:

10x+4\(\displaystyle 10x+4\)

10x^{2}+4\(\displaystyle 10x^{2}+4\)

25x^{2}+4\(\displaystyle 25x^{2}+4\)

25x^{2}+10x+4\(\displaystyle 25x^{2}+10x+4\)

25x^{2}+20x+4\(\displaystyle 25x^{2}+20x+4\)

Correct answer:

25x^{2}+20x+4\(\displaystyle 25x^{2}+20x+4\)

Explanation:

(5x+2)^{2}\(\displaystyle (5x+2)^{2}\) is equivalent to (5x+2)(5x+2)\(\displaystyle (5x+2)(5x+2)\).

Using the FOIL method, you multiply the first number of each set 5x\cdot 5x=25x^{2}\(\displaystyle 5x\cdot 5x=25x^{2}\), multiply the outer numbers of each set 5x\cdot 2=10x\(\displaystyle 5x\cdot 2=10x\), multiply the inner numbers of each set 2\cdot 5x=10x\(\displaystyle 2\cdot 5x=10x\), and multiply outer numbers of each set 2\cdot 2=4\(\displaystyle 2\cdot 2=4\).

Adding all these numbers together, you get 25x^{2}+10x+10x+4=25x^{2}+20x+4\(\displaystyle 25x^{2}+10x+10x+4=25x^{2}+20x+4\)

Example Question #1 : Exponents And The Distributive Property

\(\displaystyle (4x-9)^{3}=?\)

 

Possible Answers:

\(\displaystyle 64x^3-729\)

\(\displaystyle 12x-27\)

\(\displaystyle 12x^3-27\)

\(\displaystyle 64x^3-432x^2+972x-729\)

Correct answer:

\(\displaystyle 64x^3-432x^2+972x-729\)

Explanation:

FOIL the first two terms:

\(\displaystyle (4x-9)(4x-9)=16x^2-36x-36x+81 = 16x^2-72x+81\)

Next, multiply this expression by the last term:

\(\displaystyle (16x^2-72x+81)(4x-9)=64x^3-144x^2-22x^2+648x+324x-729\)

Finally, combine the terms:

\(\displaystyle (4x-9)^3=64x^3-432x^2+972x-729\)

 

 

Example Question #73 : Exponents

If \(\displaystyle q=2\), what is the value of the equation \(\displaystyle q(q-7)^{2}\)?

 

Possible Answers:

\(\displaystyle 100\)

\(\displaystyle 25\)

\(\displaystyle 50\)

\(\displaystyle 10\)

\(\displaystyle -50\)

Correct answer:

\(\displaystyle 50\)

Explanation:

Plug in \(\displaystyle 2\) for \(\displaystyle q\) in the equation \(\displaystyle q(q-7)^{2}\)

That gives: \(\displaystyle 2(2-7)^{2}\)

Then solve the computation inside the parenthesis: \(\displaystyle 2(-5)^{2}\)

The answer should then be \(\displaystyle 50\)

 

 

Example Question #2 : How To Use Foil With Exponents

The expression \(\displaystyle (4x^3-2)(9x^6+7)\) is equivalent to __________.

Possible Answers:

\(\displaystyle 36x^{18}-18x^6+28x^3-14\)

\(\displaystyle 4x^9-18x^6+28x^3-14\)

\(\displaystyle 36x^9-18x^6+28x^3-14\)

\(\displaystyle 36x^9-18x^6-28x^3+14\)

\(\displaystyle 9x^9-2x^6+7x^3-14\)

Correct answer:

\(\displaystyle 36x^9-18x^6+28x^3-14\)

Explanation:

Use FOIL and be mindful of exponent rules. Remember that when you multiply two terms with the same bases but different exponents, you will need to add the exponents together.

Foilexpo

 

Example Question #3 : How To Use Foil With Exponents

The expression \(\displaystyle (3x^2+x)(4x^3+2x)\) is equivalent to __________.

Possible Answers:

\(\displaystyle 12x^5+10x^4+6x^3+2x^2\)

\(\displaystyle 12x^5+4x^4+8x^2\)

\(\displaystyle 12x^6+4x^3+6x^2+2x\)

\(\displaystyle 12x^5+4x^4+6x^3+6x^2\)

\(\displaystyle 12x^5+4x^4+6x^3+2x^2\)

Correct answer:

\(\displaystyle 12x^5+4x^4+6x^3+2x^2\)

Explanation:

Remember to add exponents when two terms with like bases are being multiplied.

 

Foilexpo

Example Question #3 : How To Use Foil With Exponents

Use the FOIL method to simplify the following expression:

\(\displaystyle (x^3+2x^2)^2\)

Possible Answers:

\(\displaystyle 4x^5+4\)

\(\displaystyle x^6+2x^4\)

\(\displaystyle x^6+4x^5+4x^4\)

\(\displaystyle 5x^6+4x^4\)

\(\displaystyle x^6+4x^4\)

Correct answer:

\(\displaystyle x^6+4x^5+4x^4\)

Explanation:

Use the FOIL method to simplify the following expression:

\(\displaystyle (x^3+2x^2)^2\)

Step 1: Expand the expression.

\(\displaystyle (x^3+2x^2)(x^3+2x^2)\)

Step 2: FOIL

First: \(\displaystyle x^3\cdot x^3 = x^6\)

Outside: \(\displaystyle x^3 \cdot 2x^2 =2x^5\)

Inside: \(\displaystyle 2x^2 \cdot x^3 = 2x^5\)

Last: \(\displaystyle 2x^2 \cdot 2x^2 = 4x^4\)

Step 2: Sum the products.

\(\displaystyle x^6+2x^5+2x^5+4x^4\)

\(\displaystyle x^6+4x^5+4x^4\)

Example Question #81 : Exponents

The rule for adding exponents is \(\displaystyle a^m + a^n = a^{m+n}\).

The rule for multiplying exponents is \(\displaystyle (a^m)^n = a^{m\cdot n}\).

Terms with matching variables AND exponents are additive.

Multiply: \(\displaystyle (a^3 + b^2c^2) \cdot (a^7 + bc^3)\)

Possible Answers:

\(\displaystyle a^{10} + a^{10}b^3c^5 + b^3c^5\)

\(\displaystyle a^{10} + b^3c^5\)

\(\displaystyle a^{21}+b^2c^6\)

\(\displaystyle a^{10} + a^7b^2c^2 + a^3bc^3 + b^3c^5\)

\(\displaystyle a^{10} + a^21b^2c^6 + b^3c^5\)

Correct answer:

\(\displaystyle a^{10} + a^7b^2c^2 + a^3bc^3 + b^3c^5\)

Explanation:

Using FOIL on \(\displaystyle (a^3 + b^2c^2) \cdot (a^7 + bc^3)\), we see that:

First: \(\displaystyle a^3 \cdot a^7 = a^{10}\)

Outer: \(\displaystyle a^3 \cdot bc^3 = a^3bc^3\)

Inner: \(\displaystyle b^2c^2 \cdot a^7 = a^7b^2c^2\)

Last: \(\displaystyle b^2c^2 \cdot bc^3 = b^3c^5\)

Note that the middle terms are not additive: while they share common variables, they do not share matching exponents.

Thus, we have \(\displaystyle a^{10} + a^7b^2c^2 + a^3bc^3 + b^3c^5\). The arrangement goes by highest leading exponent, and alphabetically in the case of the last two terms.

Example Question #5 : Exponents And The Distributive Property

The concept of FOIL can be applied to both an exponential expression and to an exponential modifier on an existing expression.

For all \(\displaystyle x\)\(\displaystyle (3x^3 + 7x^2)^2\) = __________.

Possible Answers:

\(\displaystyle 9x^3 + 49x^2\)

\(\displaystyle 9x^6 + 42x^5 + 49x^4\)

\(\displaystyle 3x^6 + 7x^9\)

\(\displaystyle 9x^6 + 21x^{10} + 49x^4\)

\(\displaystyle 9x^6 + 49x^4\)

Correct answer:

\(\displaystyle 9x^6 + 42x^5 + 49x^4\)

Explanation:

Using FOIL, we see that \(\displaystyle (3x^3 + 7x^2)^2 = (3x^3 + 7x^2) \cdot(3x^3 + 7x^2)\)

First = \(\displaystyle 3x^3 \cdot 3x^3 = 9x^6\)

Outer = \(\displaystyle 3x^3 \cdot 7x^2 = 21x^5\)

Inner = \(\displaystyle 7x^2 \cdot 3x^3 = 21x^5\)

Last = \(\displaystyle 7x^2 \cdot 7x^2 = 49x^4\)

Remember that terms with like exponents are additive, so we can combine our middle terms:

\(\displaystyle 21x^5 + 21x^5 = 42x^5\)

Now order the expression from the highest exponent down:

\(\displaystyle 9x^6 + 42x^5 + 49x^4\)

Thus,

\(\displaystyle (3x^3 + 7x^2)^2 = 9x^6 + 42x^5 + 49x^4\)

Example Question #3 : How To Use Foil With Exponents

Square the binomial.

\(\displaystyle (x^{2}y^{4}+xy^{6})^{2}\)

Possible Answers:

\(\displaystyle x^4y^{16}+2x^2y^{24}+xy^{36}\)

\(\displaystyle x^4y^8+2x^3y^{10}+x^2y^{12}\)

\(\displaystyle x^{4}y^{8}+x^{2}y^{12}\)

\(\displaystyle 2x^{8}y^{20}\)

\(\displaystyle x^8y^8+x^2y^{12}\)

Correct answer:

\(\displaystyle x^4y^8+2x^3y^{10}+x^2y^{12}\)

Explanation:

\(\displaystyle (x^{2}y^{4}+xy^{6})^{2}\)

\(\displaystyle (x^{2}y^{4}+xy^{6})(x^{2}y^{4}+xy^{6})\)

We will need to FOIL.

First: \(\displaystyle x^2y^4*x^2y^4=x^4y^8\)

Inside: \(\displaystyle xy^6*x^2y^4=x^3y^{10}\)

Outside: \(\displaystyle x^2y^4*xy^6=x^3y^{10}\)

Last: \(\displaystyle xy^6*xy^6=x^2y^{12}\)

Sum all of the terms and simplify.

\(\displaystyle x^4y^8+x^3y^{10}+x^3y^{10}+x^2y^{12}\)

\(\displaystyle x^4y^8+2x^3y^{10}+x^2y^{12}\)

Example Question #3 : Exponents And The Distributive Property

Simplify:

\(\displaystyle (xy^2 + 2x^3y^2)(xy^3+3x^2)\)

Possible Answers:

\(\displaystyle x^2y^5+ 3x^3y^2 + 2x^4y^5 + 6x^5y^2\)

\(\displaystyle xy^6 + 3x^2y^2 + 2x^3y^6+6x^6y^2\)

\(\displaystyle 6x^2y^4+ 2x^3y^2 + 3x^2y^2\)

\(\displaystyle 11x^1^4y^1^6\)

\(\displaystyle 3x^4y^5+ x^3y^2 + 2xy^5 + 3x^5y^2\)

Correct answer:

\(\displaystyle x^2y^5+ 3x^3y^2 + 2x^4y^5 + 6x^5y^2\)

Explanation:

First, merely FOIL out your values.  Thus:

\(\displaystyle (xy^2 + 2x^3y^2)(xy^3+3x^2)\) becomes

\(\displaystyle (xy^2* xy^3+ xy^2*3x^2 + 2x^3y^2*xy^3 + 2x^3y^2*3x^2)\)

Now, just remember that when you multiply similar bases, you add the exponents.  Thus, simplify to:

\(\displaystyle x^2y^5+ 3x^3y^2 + 2x^4y^5 + 6x^5y^2\)

Since nothing can be combined, this is the final answer.

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