ACT Math : Basic Squaring / Square Roots

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #26 : Square Roots And Operations

Simplify:

\(\displaystyle \small \frac{\sqrt{1155}}{\sqrt{560}}\)

Possible Answers:

\(\displaystyle \small \frac{\sqrt{33}}{4}\)

\(\displaystyle \small \frac{7\sqrt{10}}{6}\)

\(\displaystyle \small 2\sqrt{55}\)

\(\displaystyle \small \frac{2\sqrt{77}}{3}\)

\(\displaystyle \small \frac{3\sqrt{55}}{2}\)

Correct answer:

\(\displaystyle \small \frac{\sqrt{33}}{4}\)

Explanation:

Division of square roots is easy, since you can combine the roots and treat it like any other fraction. Thus, you can convert our fraction as follows:

\(\displaystyle \small \frac{\sqrt{1155}}{\sqrt{560}} = \sqrt{\frac{1155}{560}}\)

Next, you begin to reduce the fraction:

\(\displaystyle \small \small \sqrt{\frac{1155}{560}} = \sqrt{\frac{3*5*7*11}{2*2*2*2*5*7}}\)

This reduces to:

\(\displaystyle \small \sqrt{\frac{3*11}{2*2*2*2}}\)

Now, break this apart again into:

\(\displaystyle \small \frac{\sqrt{33}}{\sqrt{16}}\), which is \(\displaystyle \small \frac{\sqrt{33}}{4}\)

Example Question #41 : Basic Squaring / Square Roots

Which of the following is equal to \(\displaystyle \sqrt{75}\) ?

Possible Answers:

\(\displaystyle 9\)

\(\displaystyle 3\sqrt{5}\)

\(\displaystyle 7.5\sqrt{10}\)

\(\displaystyle 5\sqrt{3}\)

Correct answer:

\(\displaystyle 5\sqrt{3}\)

Explanation:

√75 can be broken down to √25 * √3. Which simplifies to 5√3.

Example Question #2 : How To Simplify Square Roots

Simplify \sqrt{a^{3}b^{4}c^{5}}\(\displaystyle \sqrt{a^{3}b^{4}c^{5}}\).

Possible Answers:

a^{2}bc^{2}\sqrt{ac}\(\displaystyle a^{2}bc^{2}\sqrt{ac}\)

a^{2}bc\sqrt{bc}\(\displaystyle a^{2}bc\sqrt{bc}\)

a^{2}b^{2}c^{2}\sqrt{bc}\(\displaystyle a^{2}b^{2}c^{2}\sqrt{bc}\)

a^{2}b^{2}c\sqrt{ab}\(\displaystyle a^{2}b^{2}c\sqrt{ab}\)

ab^{2}c^{2}\sqrt{ac}\(\displaystyle ab^{2}c^{2}\sqrt{ac}\)

Correct answer:

ab^{2}c^{2}\sqrt{ac}\(\displaystyle ab^{2}c^{2}\sqrt{ac}\)

Explanation:

Rewrite what is under the radical in terms of perfect squares:

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

x^{4}=x^{2}\cdot x^{2}\(\displaystyle x^{4}=x^{2}\cdot x^{2}\)

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

Therefore, \sqrt{a^{3}b^{4}c^{5}}= \sqrt{a^{2}a^{1}b^{4}c^{4}c^{1}}=ab^{2}c^{2}\sqrt{ac}\(\displaystyle \sqrt{a^{3}b^{4}c^{5}}= \sqrt{a^{2}a^{1}b^{4}c^{4}c^{1}}=ab^{2}c^{2}\sqrt{ac}\).

Example Question #3 : How To Simplify Square Roots

What is \(\displaystyle \sqrt{50}\)?

Possible Answers:

\(\displaystyle 10\sqrt{2}\)

\(\displaystyle 2\sqrt{5}\)

\(\displaystyle 5\sqrt{2}\)

\(\displaystyle 5\)

\(\displaystyle 10\)

Correct answer:

\(\displaystyle 5\sqrt{2}\)

Explanation:

We know that 25 is a factor of 50. The square root of 25 is 5. That leaves \(\displaystyle \sqrt{2}\) which can not be simplified further.

Example Question #4 : How To Simplify Square Roots

Which of the following is equivalent to \frac{x + \sqrt{3}}{3x + \sqrt{2}}\(\displaystyle \frac{x + \sqrt{3}}{3x + \sqrt{2}}\)?

Possible Answers:

\frac{3x^{2} + \sqrt{6}}{3x - 2}\(\displaystyle \frac{3x^{2} + \sqrt{6}}{3x - 2}\)

\frac{3x^{2} + 3x\sqrt{2} + x\sqrt{3} +\sqrt{6}}{9x^{2} - 2}\(\displaystyle \frac{3x^{2} + 3x\sqrt{2} + x\sqrt{3} +\sqrt{6}}{9x^{2} - 2}\)

\frac{3x^{2} - \sqrt{6}}{9x^{2} + 2}\(\displaystyle \frac{3x^{2} - \sqrt{6}}{9x^{2} + 2}\)

\frac{4x + \sqrt{5}}{3x + 2}\(\displaystyle \frac{4x + \sqrt{5}}{3x + 2}\)

\frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\(\displaystyle \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\)

Correct answer:

\frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\(\displaystyle \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\)

Explanation:

Multiply by the conjugate and the use the formula for the difference of two squares:

\frac{x + \sqrt{3}}{3x + \sqrt{2}}\(\displaystyle \frac{x + \sqrt{3}}{3x + \sqrt{2}}\)

\(\displaystyle =\) \frac{x + \sqrt{3}}{3x + \sqrt{2}}\cdot \frac{3x - \sqrt{2}}{3x - \sqrt{2}}\(\displaystyle \frac{x + \sqrt{3}}{3x + \sqrt{2}}\cdot \frac{3x - \sqrt{2}}{3x - \sqrt{2}}\)

\(\displaystyle =\) \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{(3x)^{2} - (\sqrt{2})^{2}}\(\displaystyle \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{(3x)^{2} - (\sqrt{2})^{2}}\) 

\(\displaystyle =\) \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\(\displaystyle \frac{3x^{2} -x \sqrt{2} + 3x\sqrt{3} - \sqrt{6}}{9x^{2} - 2}\)

Example Question #2 : Properties Of Roots And Exponents

Which of the following is the most simplified form of:

\(\displaystyle \sqrt{468}\)

 

Possible Answers:

\(\displaystyle 4\sqrt{29}\)

\(\displaystyle 17\sqrt{2}\)

\(\displaystyle \sqrt{468}\)

\(\displaystyle 6\sqrt{13}\)

\(\displaystyle 2\sqrt{117}\)

Correct answer:

\(\displaystyle 6\sqrt{13}\)

Explanation:

First find all of the prime factors of \(\displaystyle 468\)

\(\displaystyle 468=6\ast78=6\ast6\ast13=2\ast3\ast2\ast3\ast13\)

So \(\displaystyle \sqrt{468}=\sqrt{2\ast2\ast3\ast3\ast13}=2\ast3\sqrt{13}=6\sqrt{13}\)

Example Question #112 : Arithmetic

What is \(\displaystyle \sqrt{432}\) equal to?

Possible Answers:

\(\displaystyle 144\sqrt{3}\)

\(\displaystyle 12\sqrt{12}\)

\(\displaystyle 6\sqrt{3}\)

\(\displaystyle 6\sqrt{4}\)

\(\displaystyle 12\sqrt{3}\)

Correct answer:

\(\displaystyle 12\sqrt{3}\)

Explanation:

\(\displaystyle \sqrt{432}\)

 

1. We know that \(\displaystyle 432=(144)(3)\), which we can separate under the square root:

\(\displaystyle \sqrt{144\cdot 3}\)

 

2. 144 can be taken out since it is a perfect square: \(\displaystyle 12\cdot12=144\). This leaves us with:

\(\displaystyle 12\sqrt{3}\)

This cannot be simplified any further.

Example Question #2 : Simplifying Square Roots

Which of the following is equal to \(\displaystyle \small \sqrt{420}\)?

Possible Answers:

\(\displaystyle \small 28\sqrt{5}\)

\(\displaystyle \small 2\sqrt{105}\)

\(\displaystyle \small \small 3\sqrt{70}\)

\(\displaystyle \small 4\sqrt{35}\)

\(\displaystyle \small 6\sqrt{35}\)

Correct answer:

\(\displaystyle \small 2\sqrt{105}\)

Explanation:

When simplifying square roots, begin by prime factoring the number in question. For \(\displaystyle \small 420\), this is:

\(\displaystyle \small 420 = 2*2*3*5*7\)

Now, for each pair of numbers, you can remove that number from the square root. Thus, you can say:

\(\displaystyle \small \small \sqrt{420}=2\sqrt{105}\)

Another way to think of this is to rewrite \(\displaystyle \small \small \sqrt{420}\) as \(\displaystyle \small \sqrt{4}*\sqrt{105}\). This can be simplified in the same manner.

Example Question #4 : Simplifying Square Roots

Which of the following is equivalent to \(\displaystyle \small \sqrt{700700}\)?

Possible Answers:

\(\displaystyle \small 121\sqrt{7}\)

\(\displaystyle \small 90\sqrt{11}\)

\(\displaystyle \small 770\sqrt{13}\)

\(\displaystyle \small 100\sqrt{77}\)

\(\displaystyle \small 70\sqrt{143}\)

Correct answer:

\(\displaystyle \small 70\sqrt{143}\)

Explanation:

When simplifying square roots, begin by prime factoring the number in question. This is a bit harder for \(\displaystyle \small 700700\). Start by dividing out \(\displaystyle \small 100\):

\(\displaystyle \small 700700 = 7007 * 100\)

Now, \(\displaystyle \small 7007\) is divisible by \(\displaystyle 7\), so:

\(\displaystyle \small \small 700700 =1001 * 7 * 2*2*5*5\)

\(\displaystyle \small 1001\) is a little bit harder, but it is also divisible by \(\displaystyle \small 7\), so:

\(\displaystyle \small 700700 =143*7 * 7 * 2*2*5*5\)

With some careful testing, you will see that \(\displaystyle \small 143 = 11 * 13\)

Thus, we can say:

\(\displaystyle \small \small 700700 = 2*2*5*5*7 * 7*11*13\)

Now, for each pair of numbers, you can remove that number from the square root. Thus, you can say:

\(\displaystyle \small \small \sqrt{700700} = 2*5*7*\sqrt{143}=70\sqrt{143}\)

Another way to think of this is to rewrite \(\displaystyle \small \small \small \sqrt{700700}\) as \(\displaystyle \small \sqrt{4} * \sqrt{25} * \sqrt{49} * \sqrt{143}\). This can be simplified in the same manner.

Example Question #2 : Simplifying Square Roots

What is the simplified (reduced) form of \(\displaystyle \sqrt{96}\)?

Possible Answers:

\(\displaystyle 8\sqrt{3}\)

It cannot be simplified further.

\(\displaystyle 2\sqrt{24}\)

\(\displaystyle 4\sqrt{6}\)

\(\displaystyle 2\sqrt{48}\)

Correct answer:

\(\displaystyle 4\sqrt{6}\)

Explanation:

To simplify a square root, you have to factor the number and look for pairs. Whenever there is a pair of factors (for example two twos), you pull one to the outside.

Thus when you factor 96 you get
\(\displaystyle \\ \sqrt{96}=\sqrt{2\cdot 2\cdot 2\cdot2\cdot2\cdot 3}\\ \\=2\cdot 2\sqrt{2\cdot 3}\\ \\=4\sqrt{6}\)

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