Question

if 9(x − y)^2
= 135 and x^
2 + y^
2 = 78, find the value of xy.​

Answer 1

Answer:

Step-by-step explanation:

   9(x − y)^2  = 135

   9(x^2 +y^2 -2xy) = 135

    9x^2 + 9y^2 -18 xy = 135         equation 1

&    x^2 + y^2 = 78

       9x^2 + 9y^2            = 702

-     ( 9x^2 + 9y^2 -18 xy = 135)         (from equation 1)

   ---------------------------------------------

        0  +    0     +  18xy = 567

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                                xy = 567/18 = 31.5