Could you help me: "solve 2x² + 5x - 3 > 0", please

*solved*
This is what I have got so far but only have 2/3 marks on mathswatch, what is needed to get the third mark - cheers :smile:

(2x-1)(x+3)>0
x > 0.5
x > -3

(edited 5 years ago)

Currently doing it!

Original post by jadonim

This is what I have got so far but only have 2/3 marks on mathswatch, what is needed to get the third mark - cheers :smile:

(2x-1)(x+3)>0
x > 0.5
x > -3

This is a whole topic in GCSE called "quadratic inequalities". By the way you've finished it, it looks to me that you don't know how to do this topic and are guessing a method. Try watching this video for an explanation.

Reply 3

RDKGames

Study Forum Helper

Original post by jadonim

This is what I have got so far but only have 2/3 marks on mathswatch, what is needed to get the third mark - cheers :smile:

(2x-1)(x+3)>0
x > 0.5
x > -3

For

ab > 0

must have either

Case (A) :

a>0

and

b > 0

.

OR

Case (B) :

a < 0

and

b < 0

.

What you've done is case (A) and haven't considered case (B). And from the way I formulate this, I hope you can see that your answer should instead be:

x > 0.5

and

x > -3

. These are both satisfied when

x > 0.5

... hence this is the answer to case (A).

Reply 4

RDKGames

Study Forum Helper

Original post by izaakha

It isn't complete as for the Edexcel and AQA exam boards a graph needs to be drawn. I am currently doing my GCSE's also, so I can speak in plain English; unlike others.

So,

1. You have expanded the brackets correctly
2. Then draw the graph ( I have attached mine)
3. Then x must be between the graph so x is more than -3 but less than 0.5
4. So the correct notation is -3 < x < 0.5

That's not right.

Obviously in that region your graph obtains -ve values of y, not +ve like we want it to.

And also, don't post full solutions.

(edited 5 years ago)

Reply 5

Notnek

Original post by izaakha

It isn't finished as both Edexcel and AQA usually require a graph to be drawn and a combined inequality to be given as the final answer. This user clearly does know how to do the unit and doesn't need floccinaucinihilipilification comments like yours that belittle others.

- A graph does not need to be drawn to get the marks
- The solution you gave to the student is wrong so will only confuse them
- A video is the best way to get them to learn how to do this topic

Reply 6

QueenTbiomed

Perhaps you've lost a mark due to not showing working? It's been a long time since I did GCSEs but from what I remember, we lost marks for not showing the middle step, which in this case is:

(2x-1) > 0, 2x > 1 so x > 0.5

(x+3) > 0, so x > -3

Not sure if this still applies but I lost many silly marks just for not showing obvious working.

Original post by jadonim

This is what I have got so far but only have 2/3 marks on mathswatch, what is needed to get the third mark - cheers :smile:

(2x-1)(x+3)>0
x > 0.5
x > -3

Reply 7

jadonim

Cheers for all your help lads.
Just finished it:
(2x-1)(x+3)>0
x = 0.5
x = -3
x > 0.5
x < -3

Reply 8

izaakha

So was it asking for an exact solution? I do apologise for telling you an incorrect form of the answer before, I am also doing my GCSE's this year.

Original post by jadonim

Cheers for all your help lads.
Just finished
(2x-1)(x+3)>0
x = 0.5
x = -3
x > 0.5
x < -3

Reply 9

jadonim

Nah I just didn't understand it too well it seems, so ended up with a *****y answer, video on mathswatch wasn't helping for **** (for me anyway). I had to sketch the graph on some paper to actually get a better understanding of what the graph looked like. Technically I just had the wrong sign in "x > 3" as it shoulda been "x < 3", but really I just didn't understand it in the first place. Cheers for tryna help anyway, and there's really no need to apologize - got there in the end ; )

Original post by izaakha

So was it asking for an exact solution? I do apologise for telling you an incorrect form of the answer before, I am also doing my GCSE's this year.