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Mathematics 7 Online
OpenStudy (amtran_bus):

College algebra

OpenStudy (amtran_bus):

ganeshie8 (ganeshie8):

\(\large x^2-6x >4x-x^2 \) add \(x^2\) both sides

OpenStudy (amtran_bus):

the reason I reposted was because my answer is not matching what was on the other post.

ganeshie8 (ganeshie8):

its fine

OpenStudy (amtran_bus):

2x^2 -6x greater than 4x

ganeshie8 (ganeshie8):

\(\large x^2-6x >4x-x^2 \) add \(x^2\) both sides \(\large 2x^2-6x > 4x \)

ganeshie8 (ganeshie8):

subtract 4x both sides, so that we can see a clean quadratic

OpenStudy (amtran_bus):

\[2x^2-10x >0\]

ganeshie8 (ganeshie8):

\(\large x^2-6x >4x-x^2 \) add \(x^2\) both sides \(\large 2x^2-6x > 4x \) subtract \(4x\) both sides \(\large 2x^2-10x > 0 \)

ganeshie8 (ganeshie8):

divide 2 thru out

OpenStudy (amtran_bus):

I did not know you could do that because it was 10x.

ganeshie8 (ganeshie8):

\(\large x^2-6x >4x-x^2 \) add \(x^2\) both sides \(\large 2x^2-6x > 4x \) subtract \(4x\) both sides \(\large 2x^2-10x > 0 \) divide 2 thru out \(\large x^2-5x > 0 \)

OpenStudy (amtran_bus):

ok

ganeshie8 (ganeshie8):

\(\large x^2-6x >4x-x^2 \) add \(x^2\) both sides \(\large 2x^2-6x > 4x \) subtract \(4x\) both sides \(\large 2x^2-10x > 0 \) divide 2 thru out \(\large x^2-5x > 0 \) factor \(x\) \(\large x(x-5) > 0 \)

ganeshie8 (ganeshie8):

ab > 0 means 1) a > 0, b >0 2) a < 0, b <0

ganeshie8 (ganeshie8):

right ?

OpenStudy (amtran_bus):

Yes Sir

ganeshie8 (ganeshie8):

lol ok im no sir but ok

OpenStudy (amtran_bus):

*blush* sorry.

ganeshie8 (ganeshie8):

so, we got x(x-5) > 0 case I :- x > 0 , x-5 > 0 case II :- x < 0, x-5 < 0

ganeshie8 (ganeshie8):

work both cases

OpenStudy (amtran_bus):

Done and done

OpenStudy (amtran_bus):

Thanks so much

ganeshie8 (ganeshie8):

perfect !

OpenStudy (amtran_bus):

Nice.

ganeshie8 (ganeshie8):

case I :- x > 0 , x-5 > 0 x >0, x > 5 x > 5 **************** SOLUTION case II :- x < 0, x-5 < 0 x < 0, x < 5 x < 0 ********* solution

ganeshie8 (ganeshie8):

those two slutions give us :- x > 5 : (5, infty) x < 0 : (-infty, 0) when u combine, we get watever the anwer u showed

OpenStudy (amtran_bus):

@ganeshie8 , one question to your last 2 posts. On case 1, why did you pick the 5 as the solution and and on case 2 pick 0? Why could you not have don the reverse?

OpenStudy (amtran_bus):

Sorry for all the ?'s but I just noticed it.

ganeshie8 (ganeshie8):

Very good question ! ping me when you're on, we'll discuss :)

OpenStudy (amtran_bus):

@ganeshie8 , I got your message.

ganeshie8 (ganeshie8):

okie glad to hear :) so u did get why x >0, x > 5 becomes x > 5

OpenStudy (amtran_bus):

Well, it would not hurt to go ahead and show me.

OpenStudy (amtran_bus):

Wait, yea I understand that.

ganeshie8 (ganeshie8):

lol nothing to show as such, just we need to pick the thing that SATISFIES both

OpenStudy (amtran_bus):

\[x-5>0\] x is greater than 5

ganeshie8 (ganeshie8):

x >0, AND x > 5 x > 0 wont satisfy x > 5, but x >5 will satisfy both x>0 and x > 5 thats why we picked x > 5

OpenStudy (amtran_bus):

So let me ask this. A way to determine it could be to plug in a number greater than AND less than zero. Whichever satisfies the original equation \[x(x-5)>0\] is the one to pick.

OpenStudy (amtran_bus):

So, negative 1 would satisfy that. Thus, x has to be less than zero.

OpenStudy (amtran_bus):

As for checking if x is greater than 5 works, plug in 6 to see if it satisfies the original equation x(x−5)>0 So, 6 is greater than zero, it works.

ganeshie8 (ganeshie8):

all negative numbers will satisfy, cuz they make both x and (x-5) negative product of two negatives is positive

OpenStudy (amtran_bus):

Right, but that shows that \[x <0\] would in fact work.

OpenStudy (amtran_bus):

Right?

ganeshie8 (ganeshie8):

thats right ! now look for the other half

ganeshie8 (ganeshie8):

when, x >=0, wat wil work ?

OpenStudy (amtran_bus):

Pluging in 4 to \[x(x-5)>0\] would give -4. That wont work! Pluging in 5 to the same equation would give 0, so all # 5 and above!

ganeshie8 (ganeshie8):

nope

ganeshie8 (ganeshie8):

i mean, you're right, but not exactly correct

ganeshie8 (ganeshie8):

plugging in 5 wont work you need to plug a number GREATER than 5

OpenStudy (amtran_bus):

My bad, your right!

ganeshie8 (ganeshie8):

just making sure u see it lol, but i see u nailed the thing :)

OpenStudy (amtran_bus):

You don't know how much I appreciate your great help!

ganeshie8 (ganeshie8):

np :D

ganeshie8 (ganeshie8):

you're wlcme :)

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