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Studienführer > Prealgebra

Simplifying Expressions With Square Roots

Learning Outcomes

  • Simplify expressions with square roots using the order of operations
  • Simplify expressions with square roots that contain variables
 

Square Roots and the Order of Operations

When using the order of operations to simplify an expression that has square roots, we treat the radical sign as a grouping symbol. We simplify any expressions under the radical sign before performing other operations.  

example

Simplify: ⓐ 25+144\sqrt{25}+\sqrt{144} ⓑ 25+144\sqrt{25+144}. Solution
ⓐ Use the order of operations.
25+144\sqrt{25}+\sqrt{144}
Simplify each radical. 5+125+12
Add. 1717
ⓑ Use the order of operations.
25+144\sqrt{25+144}
Add under the radical sign. 169\sqrt{169}
Simplify. 1313
 

try it

[ohm_question]146635[/ohm_question] [ohm_question]146636[/ohm_question]
Notice the different answers in parts ⓐ and ⓑ of the example above. It is important to follow the order of operations correctly. In ⓐ, we took each square root first and then added them. In ⓑ, we added under the radical sign first and then found the square root.

Simplify Variable Expressions with Square Roots

Expressions with square root that we have looked at so far have not had any variables. What happens when we have to find a square root of a variable expression? Consider 9x2\sqrt{9{x}^{2}}, where x≥0x\ge 0. Can you think of an expression whose square is 9x2?9{x}^{2}? (?)2=9x2(3x)2=9x2so9x2=3x\begin{array}{ccc}\hfill {\left(?\right)}^{2}& =& 9{x}^{2}\hfill \\ \hfill {\left(3x\right)}^{2}& =& 9{x}^{2}\text{so}\sqrt{9{x}^{2}}=3x\hfill \end{array} When we use a variable in a square root expression, for our work, we will assume that the variable represents a non-negative number. In every example and exercise that follows, each variable in a square root expression is greater than or equal to zero.  

example

Simplify: x2\sqrt{{x}^{2}}, where x≥0x\ge 0

Answer: Solution Think about what we would have to square to get x2{x}^{2} . Algebraically, (?)2=x2{\left(?\right)}^{2}={x}^{2}

x2\sqrt{{x}^{2}}
Since (x)2=x2{\left(x\right)}^{2}={x}^{2} xx

 

try it

[ohm_question]146637[/ohm_question]
   

example

Simplify: 16x2\sqrt{16{x}^{2}}.

Answer: Solution

16x2\sqrt{16{x}^{2}}
Since(4x)2=16x2\text{Since}{\left(4x\right)}^{2}=16{x}^{2} 4x4x

 

try it

[ohm_question]146638[/ohm_question]  
   

example

Simplify: −81y2-\sqrt{81{y}^{2}}.

Answer: Solution

−81y2-\sqrt{81{y}^{2}}
Since(9y)2=81y2\text{Since}{\left(9y\right)}^{2}=81{y}^{2} −9y-9y

 

try it

[ohm_question]146639[/ohm_question]
   

example

Simplify: 36x2y2\sqrt{36{x}^{2}{y}^{2}}.

Answer: Solution

36x2y2\sqrt{36{x}^{2}{y}^{2}}
Since(6xy)2=36x2y2\text{Since}{\left(6xy\right)}^{2}=36{x}^{2}{y}^{2} 6xy6xy

 

try it

[ohm_question]146640[/ohm_question]
 

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