Spot the equation that does NOT belong with the others

Exercise and reference answers

Questions

1. Items

   1. x² − 4 = 0
   2. x² + 4 = 0
   3. x² + 0x − 4 = 0
   4. (x-2)(x+2)=0

   Reason

   x² + 4 = 0 has no real roots; the others all have roots ±2.

   Odd item

   x² + 4 = 0