Inequality Problem

• Feb 12th 2013, 07:08 PM
stephanice
Inequality Problem
Hello, Could you help me with these two inequalities? , all of them taken of Precalculus Stewart Book, Chapter 1, Exercise 1.7.
The first is:
-2x^2 ≤ 4
The answer must be (-∞, ∞)
but I got as last result x^2 ≥ -2
and it can't be root of 2, because it would be a complex number, can I?
I can't either factorize or something else.
The second is 2/5 x + 1< 1/5 -2x
and this book only have solutions for odd numbers, this is number sixteen, I got:
10/5 x + 1 < 1-2x
x +1 < 1-2/2 x
x < 1/2
I did it wrong?
Ah I forgot it... I have doubts of when change the sign 'greater than' for 'less than"
Thanks :)
• Feb 12th 2013, 07:27 PM
Plato
Re: Inequality Problem
Quote:

Originally Posted by stephanice
Hello, Could you help me with these two inequalities? , all of them taken of Precalculus Stewart Book, Chapter 1, Exercise 1.7.
The first is:
-2x^2 ≤ 4
The answer must be (-∞, ∞)
but I got as last result x^2 ≥ -2
and it can't be root of 2, because it would be a complex number, can I?

Why are you doing any work at all?
STOP! Step back. Look at the problem.

It is true for all x.