Difference between revisions of "1970 AHSME Problems/Problem 18"

(Created page with "== Problem == <math>\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}}</math> is equal to <math>\text{(A) } 2\quad \text{(B) } 2\sqrt{3}\quad \text{(C) } 4\sqrt{2}\quad \text{(D) } \sqrt{6}...")
 
 
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\text{(E) } 2\sqrt{2}</math>
 
\text{(E) } 2\sqrt{2}</math>
  
== Solution ==
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== Solution==
<math>\fbox{C}</math>
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Square the expression:
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<math>(\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}})^2=3+\sqrt{2}-2\sqrt{(3+\sqrt{2})(3-\sqrt{2})}+3-2\sqrt{2}=6-2\sqrt{9-8}=6-2\sqrt{1}=4</math>
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<math>\Rightarrow\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}}=\sqrt{4}=2\Rightarrow\boxed{A}</math>
  
 
== See also ==
 
== See also ==
{{AHSME box|year=1970|num-b=17|num-a=19}}   
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{{AHSME 35p box|year=1970|num-b=17|num-a=19}}   
  
 
[[Category: Introductory Algebra Problems]]
 
[[Category: Introductory Algebra Problems]]
 
{{MAA Notice}}
 
{{MAA Notice}}

Latest revision as of 15:23, 2 July 2016

Problem

$\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}}$ is equal to

$\text{(A) } 2\quad \text{(B) } 2\sqrt{3}\quad \text{(C) } 4\sqrt{2}\quad \text{(D) } \sqrt{6}\quad \text{(E) } 2\sqrt{2}$

Solution

Square the expression:

$(\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}})^2=3+\sqrt{2}-2\sqrt{(3+\sqrt{2})(3-\sqrt{2})}+3-2\sqrt{2}=6-2\sqrt{9-8}=6-2\sqrt{1}=4$

$\Rightarrow\sqrt{3+2\sqrt{2}}-\sqrt{3-2\sqrt{2}}=\sqrt{4}=2\Rightarrow\boxed{A}$

See also

1970 AHSC (ProblemsAnswer KeyResources)
Preceded by
Problem 17
Followed by
Problem 19
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