Stupid math problem

[Emultra]

I can't figure out how to do this, and googling doesn't seem to help either:

Inequality: x + 1 ≥ 2/x

Can't multiply by x since I don't know whether it's positive (and thus if the sign should be flipped). What's the method to use here?

 

[skimple]

(x-1) (x+2) ≥ 0

 

[Jaepheth]

http://www.wolframalpha.com/input/?i=x+++1+≥+2/x

 

[z1ggy]

(x-1) (x+2) ≥ 0

+1

 

[Emultra]

(x-1) (x+2) ≥ 0

What's the thought process behind arriving at that, though? And for that condition I'm coming up with x &#8804; -2 and x &#8805; 1, whereas the correct answer is -2 &#8804; x < 0 and x &#8805; 1; what am I doing wrong?

 

[dighn]

What's the thought process behind arriving at that, though? And for that condition I'm coming up with x &#8804; -2 and x &#8805; 1, whereas the correct answer is -2 &#8804; x < 0 and x &#8805; 1; what am I doing wrong?

that's actually not entirely correct

x + 1 &#8805; 2/x
x + 1 - 2/x >= 0
(x^2 + x - 2) / 2 >= 0
(x + 2)(x - 1)/x >= 0

then you can multiply by x on both sides, checking both the cases of x > 0 and x < 0 separately

 

[Schfifty Five]

I can't figure out how to do this, and googling doesn't seem to help either:

Inequality: x + 1 &#8805; 2/x

Can't multiply by x since I don't know whether it's positive (and thus if the sign should be flipped). What's the method to use here?

(x+1) &#8805; 2/x;
x(x+1) &#8805; 2;
x^2 + x - 2 &#8805; 0; then factor...
(x-1)(x+2) &#8805; 0;

 

[Schfifty Five]

that's actually not entirely correct

x + 1 &#8805; 2/x
x + 1 - 2/x >= 0
(x^2 + x - 2) / 2 >= 0
(x + 2)(x - 1)/x >= 0

then you can multiply by x on both sides, checking both the cases of x > 0 and x < 0 separately

 

[rayfieldclement]

I REALLY DISLIKE math.

 

[radhak]

I can't figure out how to do this, and googling doesn't seem to help either:

Inequality: x + 1 &#8805; 2/x

Can't multiply by x since I don't know whether it's positive (and thus if the sign should be flipped). What's the method to use here?

x can be both positive and negative.
Do it in two steps:

a. When x is positive,
x ( x + 1) &#8805; 2
=> x² + x - 2 &#8805; 0
=> (x -1 ) (x + 2) &#8805; 0

which gives a specific graph, one side of which is a solution space.

b. When x is negative,
x ( x + 1) &#8804; 2
=> x² + x - 2 &#8804; 0
=> (x - 1 ) (x + 2) &#8804; 0
which gives another graph that marks the boundary of what is also the solution space.

I think the WolframAlpha link above gives you the resultant graph.

And yes, you'd also find that -2 &#8804; x < 0 and x &#8805; 1 does show up as the right solution.

 

[dighn]

(x+2)(x-1)/x >= 0 <- you can't just get rid of the x because its sign is unclear

e.g. with (x+2)(x-1) >= 0, x = -3 is a solution (-1 * -4 = 4)

but feed it into the original: x + 1 >= 2/x, you get -2 >= (-2/3) <- not true

example when x > 0
(x+2)(x-1)/x >= 0
(x+2)(x-1) >= 0

(x+2) >= 0 and (x-1) >= 0; x >= -1, x >= 1, and x > 0, so x >= 1

or

(x+2) <= 0 and (x-1) <= 0; x <= -2, x <= 1, but x is also > 0, no solution

you can do a similar check for x < 0 (just need to flip the inequality when getting rid of the /x)

 

[SphinxnihpS]

I can't figure out how to do this, and googling doesn't seem to help either:

Inequality: x + 1 &#8805; 2/x

Can't multiply by x since I don't know whether it's positive (and thus if the sign should be flipped). What's the method to use here?

Stop fucking trolling!

If you are genuinely this bad at math, do you think it's a good idea, from a social standpoint, to ask for help on a tech forum?

 

[SandEagle]

no such thing as a stupid math problem. only stupid math students.

answer is 42, btw

 

[SheHateMe]

Wow, this is 6th grade Algebra.

 

[SphinxnihpS]

Wow, this is 6th grade Algebra.

A sad fact in and of itself. This is elementary school math in most places.

 

[shortylickens]

A sad fact in and of itself. This is elementary school math in most places.

Bullshit.

I went to school in Minnesota which is rated 2nd in the country for science & math.
My district was one of the highest rated in the state.

We did basic pre-algebra in the 6th grade but we did NOT do the OP's problem.

Quit lying about the educational state of the country when you clearly dont know any better.

 

[brianmanahan]

Can't multiply by x since I don't know whether it's positive (and thus if the sign should be flipped)

lol, you dont know algebra then

 

[SphinxnihpS]

Bullshit.

I went to school in Minnesota which is rated 2nd in the country for science & math.
My district was one of the highest rated in the state.

We did basic pre-algebra in the 6th grade but we did NOT do the OP's problem.

Quit lying about the educational state of the country when you clearly dont know any better.

I said most places.

 

[SKORPI0]

Wow, this is 6th grade Algebra.

A sad fact in and of itself. This is elementary school math in most places.

This, apparently OP hasn't reached this level. j/k

 

[BladeVenom]

I REALLY DISLIKE math.

Math doesn't like you either.

 

[GoSharks]

A sad fact in and of itself. This is elementary school math in most places.

Not in America, at least when I was in grade school. I learned about 'x' in 7th grade pre-algebra. That was the advanced track too.

 

[radhak]

Wow, this is 6th grade Algebra.

A sad fact in and of itself. This is elementary school math in most places.

This, apparently OP hasn't reached this level. j/k

No it's not elementary school math. The screenshot you pasted was linear inequality. The problem in the OP is a quadratic inequality, generally appearing in pre-calculus, which means High School, though some kids do take it as part of advanced math in middle school.

 

[Emultra]

My math education has been rather sundry, so there's gaps in my knowledge. The four basic rules for inequalities, and multiplication by the LCD allow for solving a lot of inequalities, but I didn't quite get this one.

Thanks for the helpful replies.

 

[Pulsar]

My math education has been rather sundry, so there's gaps in my knowledge. The four basic rules for inequalities, and multiplication by the LCD allow for solving a lot of inequalities, but I didn't quite get this one.

Thanks for the helpful replies.

Yeah, just ignore the trolling assholes. This is not elementary school math, any many many majors that aren´t math centric may have not even taken it. This was algebra 2 in my state and if you were going into a trade school you didn't need to take it.

 

[SphinxnihpS]

Yeah, just ignore the trolling assholes. This is not elementary school math, any many many majors that aren´t math centric may have not even taken it. This was algebra 2 in my state and if you were going into a trade school you didn't need to take it.

Yeah, just ignore the trolling assholes. This is not elementary school math, any many many majors that aren´t math centric may have not even taken it. This was algebra 2 in my state and if you were going into a trade school you didn't need to take it.

Me me me me me me me...

So you're saying the status quo is good enough? We're like 40th in math among developed nations.

Let's take a different tack...

Why ISN'T this elementary school math here in the good ole USA?