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Question
If x + y = 1 and xy = -12; find:
x - y
Solution
(x + y)2 = (1)2
⇒ x2 + y2 + 2xy
= 1
⇒ x2 + y2
= 1 - 2(-12)
= 1 + 24
= 25
Now, (x - y)2
= x2 + y2 - 2xy
= 25 - 2(-12)
= 25 + 24
= 49
⇒ x - y
= ±7.
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