Need help solving/graphing some inequalities

  • Thread starter Thread starter rought
  • Start date Start date
  • Tags Tags
    Inequalities
AI Thread Summary
The discussion focuses on solving and graphing inequalities, specifically the expressions involving absolute values and polynomial inequalities. For the inequality 0 < |x + 3| < 1, the correct solution is identified as -4 < x < -2 or -3 < x < -2, which is confirmed through graphing. The second set of inequalities, 1 ≤ |X - 4| ≤ 3 and 1 ≤ |Y - 4| ≤ 3, leads to the solution ranges 1 ≤ X ≤ 3 or 5 ≤ X ≤ 7, and similarly for Y. The more complex inequality X^3 + 2x^2 > 3X + 6 requires solving the associated equation, revealing roots at -2, -√3, and √3, which help determine the sign of the polynomial across different intervals. Understanding these intervals is crucial for identifying where the original inequality holds true.
rought
Messages
34
Reaction score
0
Alright again I am having trouble with a few problems.

I am unsure on the first two problem's answers and I have no idea how to do the third one..Solve and graph the solution on a number line

0 < |x + 3| < 1

I get: -3 < X < -2 or -3 > X > -4

and it graphs like this (is this right?) [horrible picture sorry]

a47sds.png



Graph the solution set on a coordinate of axes
(I know how to graph it I am just unsure on the points)

1 ≤ |X - 4| ≤ 3

1 ≤ |Y - 4| ≤ 3

I ended up getting

5 ≤ Y ≤ 7 or 3 ≥ Y ≥ 1

and the same for X

5 ≤ X ≤ 7 or 3 ≥ X ≥ 1

Is that right? =/

Ok and this last one I have no idea how to solve :confused:

Solve: X^3 + 2x^2 > 3X + 6
 
Physics news on Phys.org
Ok I think I have the first two figured out but I am still stuck on

Solve: X^3 + 2x^2 > 3X + 6
 
The best way to solve any complicated inequality is to first solve the associated equation.

x3+ 2x2> 3x+ 6 is the same as x3+ 2x2- 3x- 6> 0 and the associated equationj is x3+ 2x2- 3x- 6= 0.

If there are any rational solutions to that they must divide 6 and so are 1, -1, 2, -2, 3, -3, 6, or -6. Trying each of those we see that (-2)3+ 2(-2)2- 3(-2)- 6= -8+ 8+ 6- 6= 0 so x= -2 is a root. Dividing by (x+ 2) we get x2- 3 as quotient and x= \pm\sqrt{3} as the other 2 roots. The numbers, -2, -\sqrt{3}, and \sqrt{3} separate all real numbers into four intervals: x< -2, -2&lt; x&lt; -\sqrt{3}, -\sqrt{3}&lt;\sqrt{3}, and \sqrt{3}&lt; x. Since the polynomial x3+ 2x2- 3x- 6 is continuous it can change sign only at those points where it is 0. Check on point in each interval to determine whether the numbers in that interval make the value positive or negative.
 
I picked up this problem from the Schaum's series book titled "College Mathematics" by Ayres/Schmidt. It is a solved problem in the book. But what surprised me was that the solution to this problem was given in one line without any explanation. I could, therefore, not understand how the given one-line solution was reached. The one-line solution in the book says: The equation is ##x \cos{\omega} +y \sin{\omega} - 5 = 0##, ##\omega## being the parameter. From my side, the only thing I could...
Back
Top