Posted by **alli** on Sunday, August 19, 2012 at 10:26pm.

solve the following inequality. write the answer in interval notation

x^3-4x^2-21x<0

please show work so i can understand this problem better! thanks

- college algebra -
**Steve**, Monday, August 20, 2012 at 12:21am
Since x^3-4x^2-21x = x(x+3)(x-7)

there are no repeated roots. So, at each root, the graph crosses the x-axis, and the function changes sign.

Starting with large negative x, all 3 factors are negative. So, on the number line, start with - signs and switch at each root:

----- -7 +++++ 0 ----- 3 +++++++

x is in (-oo,-7) U (0,3)

## Answer this Question

## Related Questions

- algebra - Solve the following inequality and write your answer using interval ...
- algebra - Solve the following inequality and write answer using interval ...
- Math- Problem3 - Solve the following inequality and write your answer using ...
- Solve Inequality - Solve the inequality. Express your solution using interval ...
- Algebra-problem restated - Solve the following inequality. (x-4)/(-x+2)>0 ...
- calculus - solve the following inequality. write your solution in interval ...
- Algebra - Solve the inequality: x+8 over x-1 > OR = 0 Write the solution set ...
- math - solve the inequality, write answer using interval notation pleas show the...
- college algebra - Solve the following inequality. x^3+9x^2-108 less or equal to ...
- Algebra - Just wondering if I did this correctly step by step. If not ...

More Related Questions