Question

If x + y = 1 and xy = -12; find:
x - y

Answer 1

(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.