# Solving inequalities algebraically

• Dec 25th 2007, 09:41 AM
xxlvh
Solving inequalities algebraically
Solve x2-x is greater than or equal to 20 algebraically; then graph your solution.

1st off, can someone suggest if I actually draw out a graph and graph it or did they mean put it on a number line?

and I don't know if I am using the correct method to solve..
x2 - x - 20 is greater than or equal to zero
(x-5)(x+4) is greater than or equal to zero
x = 5, -4

where do I go from there algebraically find the final solution?
• Dec 25th 2007, 09:46 AM
Jhevon
Quote:

Originally Posted by xxlvh
Solve x2-x is greater than or equal to 20 algebraically; then graph your solution.

1st off, can someone suggest if I actually draw out a graph and graph it or did they mean put it on a number line?

and I don't know if I am using the correct method to solve..
x2 - x - 20 is greater than or equal to zero
(x-5)(x+4) is greater than or equal to zero
x = 5, -4

Quote:

where do I go from there algebraically find the final solution?
you already found the solutions, just change them into inequalities now

they asked you to graph your solutions, not the inequalities, so a number line would be ideal. when you have the right solutons, we can take it from there
• Dec 25th 2007, 09:51 AM
xxlvh
hrmm well x - 5 > 0 so x>5 which is correct
but x + 4 >0 turning to x>-4 isn't right it should be x<-4 how do I get that answer?
• Dec 25th 2007, 09:58 AM
Jhevon
Quote:

Originally Posted by xxlvh
hrmm well x - 5 > 0 so x>5 which is correct
but x + 4 >0 turning to x>-4 isn't right it should be x<-4 how do I get that answer?

you just change it to that answer. sometimes when solving inequalities, the signs end up turning the wrong way, even though you did nothing wrong in the algebraic manipulation. that's why you always check your answers with these, so you know you have your signs pointing the right way, as you did. now just draw those solutions on a number line