Question

If x-y=9,x²+y²=27,then xy=?​

Answer 1

xy = - 27

Explanation:

Note that

(x - y)² = x² - 2xy + y² ← substitute given values, that is

9² = 27 - 2xy

81 = 27 - 2xy ( subtract 27 from both sides )

54 = - 2xy (divide both sides by - 2 )

- 27 = xy