Q18 of 30 Page 2

If x + y = 5 and xy = 4, find x - y, using identities.

    (x - y) 2 = x2 - 2xy + y2
                 = x2 + 2xy + y2 - 4xy
                 = (x + y)2 - 4xy 
                 = 52 - 4 × 4
             = 25 - 16 = 9
 ∴  x – y = 𢆩
            = 3

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