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If x + 2y = 4 and xy = 18, what is the value of x^2 + 4y^2?

 Apr 12, 2022
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x + 2y  = 4     square both sides ⇒  x^2 + 4xy + 4y^2  = 16        (1)

xy = 18          multiply through by 4  ⇒  4xy = 72         (2)

 

Sub (2)  into (1)

 

x^2  + 72 + 4y^2  =  16     subtract 72 from both sides

 

x^2 + 4y^2  =  -56

 

cool cool cool

 Apr 12, 2022

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