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If x + 2y= 4 and xy = -8, what is the value of x^2 + 4y^2?

 May 23, 2019
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If x + 2y= 4 and xy = -8, what is the value of x^2 + 4y^2?

 

x + 2y = 4        square both sides

 

(x + 2y)^2  = 16

x^2 + 4xy + 4y^2  = 16          [xy = -8 ]

x^2 + 4(-8) + 4y^2  = 16

x^2 + 4y^2 - 32  =  16

x^2 + 4y^2  = 48

 

 

cool cool cool

 May 23, 2019

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