ACT Math : Trinomials

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #41 : Polynomials

Find the \(\displaystyle x\)-intercepts:

\(\displaystyle y=9-10x+x^{2}\)

Possible Answers:

\(\displaystyle (0,1)\) and \(\displaystyle (0,9)\)

\(\displaystyle (1,0)\) and \(\displaystyle (9,0)\)

\(\displaystyle (0,9)\) only

\(\displaystyle (0,1)\) and \(\displaystyle (0,0)\)

Correct answer:

\(\displaystyle (1,0)\) and \(\displaystyle (9,0)\)

Explanation:

\(\displaystyle x\)-intercepts occur when \(\displaystyle y=0\).

1. Set the expression equal to \(\displaystyle 0\) and rearrange:

\(\displaystyle x^{2}-10x+9=0\)

 

2. Factor the expression:

\(\displaystyle (x-1)(x-9)=0\)

 

3. Solve for \(\displaystyle x\):

\(\displaystyle x-1=0\)

\(\displaystyle x=1\)

and...

\(\displaystyle x-9=0\)

\(\displaystyle x=9\)

 

4. Rewrite the answers as coordinates:

\(\displaystyle x=9\) becomes \(\displaystyle (9,0)\) and \(\displaystyle x=1\) becomes \(\displaystyle (1,0)\).

Example Question #61 : Variables

Solve for \(\displaystyle x\) when \(\displaystyle 6x^{2}+2x-20=0\).

Possible Answers:

\(\displaystyle x=0, x=4\)

\(\displaystyle x=\frac{5}{3}, x=-2\)

\(\displaystyle x=\frac{-5}{3}, x=2\)

\(\displaystyle x=0, x=-2\)

Correct answer:

\(\displaystyle x=\frac{5}{3}, x=-2\)

Explanation:

1. Factor the expression:

\(\displaystyle 6x^{2}+2x-20= (3x-5)(2x+4)\)

 

2. Solve for \(\displaystyle x\):

\(\displaystyle 3x-5=0\)

\(\displaystyle x=\frac{5}{3}\)

and...

\(\displaystyle 2x+4=0\)

\(\displaystyle x=-2\)

Example Question #62 : Variables

Factor the following expression:

\(\displaystyle x^2-8x+15\)

Possible Answers:

\(\displaystyle (x+5)(x-3)\)

\(\displaystyle (x-5)(x-3)\)

\(\displaystyle (x+15)(x-1)\)

\(\displaystyle (x-15)(x+1)\)

\(\displaystyle (x-5)(x+3)\)

Correct answer:

\(\displaystyle (x-5)(x-3)\)

Explanation:

Remember that when you factor a trinomial in the form \(\displaystyle ax^2+bx+c\), you need to find factors of \(\displaystyle c\) that add up to \(\displaystyle b\).

First, write down all the possible factors of \(\displaystyle c\).

\(\displaystyle 1, 15\)

\(\displaystyle -1, -15\)

\(\displaystyle 3, 5\)

\(\displaystyle -3, -5\)

Then add them to see which one gives you the value of \(\displaystyle b\)

\(\displaystyle 1+15=16\)

\(\displaystyle -1-15=-16\)

\(\displaystyle 3+5=8\)

\(\displaystyle -3-5=-8\)

Thus, the factored form of the expression is \(\displaystyle (x-3)(x-5)\)

Example Question #4 : Trinomials

Factor the expression completely

\(\displaystyle 9x^{10}+18x^9-27x^8\)

Possible Answers:

\(\displaystyle 9x^8(x-3)(x-1)\)

\(\displaystyle 3x^8(x+3)(x-1)\)

\(\displaystyle 3x^8(x+3)(x+1)\)

\(\displaystyle 9x^8(x-3)(x+1)\)

\(\displaystyle 9x^8(x+3)(x-1)\)

Correct answer:

\(\displaystyle 9x^8(x+3)(x-1)\)

Explanation:

First, find any common factors. In this case, there is a common factor: \(\displaystyle 9x^8\)

\(\displaystyle 9x^8(x^2+2x-3)\)

Now, factor the trinomial.

To factor the trinomial, you will need to find factors of \(\displaystyle -3\) that add up to \(\displaystyle 2\).

List out the factors of \(\displaystyle -3\), then add them.

\(\displaystyle -1+3=2\)

\(\displaystyle 1-3=-2\)

Thus, \(\displaystyle x^2+2x-3=(x-1)(x+3)\)

Example Question #5 : Trinomials

Which expression is equivalent to the polynomial \(\displaystyle x^2+9x-10\).

Possible Answers:

\(\displaystyle (x-10)(x+1)\)

\(\displaystyle (x-5)(x-4)\)

\(\displaystyle (x-5)(x+2)\)

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

\(\displaystyle (x+10)(x-1)\)

Correct answer:

\(\displaystyle (x+10)(x-1)\)

Explanation:

This question calls for us to factor the polynomial into two binomials. Since the first term is \(\displaystyle x^2\) and the last term is a number without a variable, we know that how answer will be of the form \(\displaystyle (x+ a)(x+ b)\) where a and b are positive or negative numbers.

To find a and b we look at the second and third term. Since the second term is \(\displaystyle 9x\) we know \(\displaystyle a+b=9\). (The x comes from a and b multiplying by x and then adding with each other). The +10 term tells us that \(\displaystyle a*b=10\). Using these two pieces of information we can look at possible values. The third term tells us that 1 & -10 and -1 & 10 are the possible pairs. Now we can look and see which one adds up to make 9. This gives us the pair -1 & 10 and we plug that into the equation as a and b to get our final answer.

\(\displaystyle (x+10)(x-1)\)

Example Question #1 : How To Factor A Trinomial

Which expression is equivalent to the following polynomial: \(\displaystyle x^2+5x-14\)

Possible Answers:

\(\displaystyle (x+9)(x-4)\)

\(\displaystyle (x+14)(x-9)\)

\(\displaystyle (x+5)(x-2)\)

\(\displaystyle (x-7)(x+2)\)

\(\displaystyle (x+7)(x-2)\)

Correct answer:

\(\displaystyle (x+7)(x-2)\)

Explanation:

This question calls for us to factor the polynomial into two binomials. Since the first term is \(\displaystyle x^2\) and the last term is a number without a variable, we know that how answer will be of the form \(\displaystyle (x+ a)(x+ b)\) where a and b are positive or negative numbers.

To find a and b we look at the second and third term. Since the second term is \(\displaystyle 5x\) we know \(\displaystyle a+b=5\). (The x comes from a and b multiplying by x and then adding with each other). The -14 term tells us that \(\displaystyle a*b=-14\). Using these two pieces of information we can look at possible values. The third term tells us that 1 & -14, 2 & -7, -2 & 7, and -1 & 14 are the possible pairs. Now we can look and see which one adds up to make 5. This gives us the pair -2 & 7 and we plug that into the equation as a and b to get our final answer.

\(\displaystyle (x+7)(x-2)\)

Example Question #7 : Trinomials

Which expression is equivalent to the following polynomial: 

\(\displaystyle x^2-9x+8\)

Possible Answers:

\(\displaystyle (x-1)(x-8)\)

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

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

\(\displaystyle (x-3)(x-5)\)

\(\displaystyle (x+1)(x-8)\)

Correct answer:

\(\displaystyle (x-1)(x-8)\)

Explanation:

This question calls for us to factor the polynomial into two binomials. Since the first term is \(\displaystyle x^2\) and the last term is a number without a variable, we know that how answer will be of the form \(\displaystyle (x+ a)(x+ b)\) where a and b are positive or negative numbers.

To find a and b we look at the second and third term. Since the second term is \(\displaystyle -9x\) we know \(\displaystyle a+b=-9\). (The x comes from a and b multiplying by x and then adding with each other). The \(\displaystyle +8\) term tells us that \(\displaystyle a*b=8\). Using these two pieces of information we can look at possible values. The third term tells us that 1 & 8, 2 & 4, -2 & -4, and -1 & -8 are the possible pairs. Now we can look and see which one adds up to make -9. This gives us the pair -1 & -8 and we plug that into the equation as a and b to get our final answer.

\(\displaystyle (x-1)(x-8)\)

Example Question #1 : How To Multiply Trinomials

Simplify the following:

\(\displaystyle (x^2-3x+1)(2x^2+4x-6)\)

Possible Answers:

\(\displaystyle 2x^3-14x^2+22x-12\)

\(\displaystyle 2x^4-2x^3-16x^2+22x-6\)

\(\displaystyle x^4-6x^3-16x^2+20x-6\)

\(\displaystyle x^4-2x^3-16x^2-6\)

Correct answer:

\(\displaystyle 2x^4-2x^3-16x^2+22x-6\)

Explanation:

To multiply trinomials, simply foil out your factored terms by multiplying each term in one trinomial to each term in the other trinomial. I will show this below by spliting up the first trinomial into its 3 separate terms and multiplying each by the second trinomial.

\(\displaystyle x^2(2x^2+4x-6)-3x(2x^2+4x-6)+1(2x^2+4x-6)\)

Now we treat this as the addition of three monomials multiplied by a trinomial.

\(\displaystyle 2x^4+4x^3-6x^2-6x^3-12x^2+18x+2x^2+4x-6\)

Now combine like terms and order by degree, largest to smallest.

\(\displaystyle 2x^4-2x^3-16x^2+22x-6\)

Example Question #1 : How To Multiply Trinomials

Solve: \(\displaystyle 5(x+y+z)\)

Possible Answers:

\(\displaystyle x+y+5z\)

\(\displaystyle x+y+z\)

\(\displaystyle 5x+5y+5z\)

\(\displaystyle x+5y+z\)

\(\displaystyle 5x+y+z\)

Correct answer:

\(\displaystyle 5x+5y+5z\)

Explanation:

The \(\displaystyle 5\) is distributed and multiplied to each term \(\displaystyle x\)\(\displaystyle y\), and \(\displaystyle z\).

Example Question #1 : How To Multiply Trinomials

Which of the following is equal to \(\displaystyle 7(x+y)+8(z)\)?

Possible Answers:

\(\displaystyle 15x+15y+15z\)

\(\displaystyle x+7y+8z\)

\(\displaystyle 7x+7y+8z\)

\(\displaystyle x+y+56z\)

\(\displaystyle 7x+y+8z\)

Correct answer:

\(\displaystyle 7x+7y+8z\)

Explanation:

\(\displaystyle 7\) is multiplied to both \(\displaystyle x\) and \(\displaystyle y\) and \(\displaystyle 8\) is only multiplied to \(\displaystyle z\).

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