Question

if xy =9 and x-y=7, what is the answer to x2+y2

Answer 1

x-y=7

xy=9

(x-y)^2=x^2 + y^2 - 2xy

(7)^2 = x^2 + y^2 - 2(9)

49 = x2 + y2 - 18

49+18 = x^2 + y^2

           =67

Answer 2

XY=9

so x-y=7

X=7+y

XY=9

7y+y^2 =9

y^2+7y-9=0

y=-7±√85/2

x-y=7

7±√85/2-7

7±√85/2 =X

x^2+y^2

98+170/4

=67

so ans is 67

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