Morgoth wrote:is x < 1 ?
1) x^-1/3 < 1
2) x^-2 < 1
1) x^-1/3 < 1:
Consider the domains of x < 0, 0 < x < 1, and x >= 1
Where x < 0, x^1/3 is -ve, so its reciprocal is also negative, and therefore less than one.
For 0 < x < 1, 0 < x^1/3 < 1, so x^-1/3 is > 1
For x > 1, x^1/3 > 1 so x^-1/3 is < 1
When x = 0 or x = 1, x^-1/3 = 1
So if x^-1/3 < 1, either x > 1 or x < 0, INSUFFICIENT
2) x^-2 < 1
If x > 1, x^2 > 1, so x^-2 < 1
If 0 > x > 1, then 0 < x^2 < 1, so x^-2 > 1
If -1 < x < 0, then 0 < x^2 < 1, so x^-2 > 1
If x < -1 then x^2 > 1, so x^-2 < 1
If x = -1, x = 0, or x = 1 then x^2 = 1, so X^-2 = 1
So if x^-2 < 1, then x < -1 or x > 1, INSUFFICIENT
1 & 2: Since x = -2 or x = 2 would both satisfy 1 & 2 but not determine the question, it's E.