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If $(x + y)^2 = 105$ and $x^2 + y^2 = 65$, what is the value of $xy$?

 Jun 15, 2019
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If (x + y)^2 = 105 and x^2 + y^2 = 65, what is the value of xy?

 

(x + y)^2  = 105

 

x^2 + 2xy + y^2  = 105  

 

(x^2 + y^2)   + 2xy  = 105

 

(65) + 2xy  = 105    subtract 65 from both sides

 

2xy =  40              divide both sides by 2

 

xy =  20

 

 

cool cool cool

 Jun 15, 2019

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