Expert: Abe Mantell - 1/5/2011

Question
What is x squared-1 is greater than or equal to 0?

Answer
x^2 - 1 >= 0, factor the left hand side

(x+1)(x-1) >= 0,

The only way the product of two numbers can be greater than
or equal to zero, is if they are both greater than or equal
to zero, or both less than or equal to zero.

Case I: Both  >= 0
That means the smaller one must be >=, thus x-1 >= 0 ==> x >= 1

Case II: Both <= 0
That means the larger one is <=, thus x+1 <= 0 ==> x <= -1

Final answer: x<=-1 or x>=1

Abe