Inequalities and markschemes

[12345678]

Hello, I was just wondering if somebody could clarify this please.

I solved an inequalities question and my answer was : x > -3, x < -5.

I rewrote this to -3 < x < -5.

However, the mark scheme gives the answer as ' x > -3, x < -5, no and, strict inequality signs and not wrapped'.

I was wondering what the not wrapped bit meant and if my answer is subsequently wrong?

If it makes a difference I was solving x^2 + 8x + 15 > 0.

Cheers.

 

[Quaid]

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I solved an inequalities question and my answer was : x > -3, x < -5.

I rewrote this to -3 < x < -5

answer [given] as 'x > -3, x < -5, no and, strict inequality signs and not wrapped'

Hi 12345678,

Writing -3 < x < -5 means that x is less than -5 AND greater than -3 simultaneously. (That's impossible.)

So, the "no and" part of the machine response means that you need to change AND to OR. We can use the U set operator for that, or we can write the solution as follows.

x < -5 OR x > -3

The strict inequality signs are correct, so I don't know why the machine mentions them.

Somebody else will need to explain for us the meaning of "not wrapped".

There are at least three different notations for writing answers like this (i.e., union of two sets of numbers). What notation has your class been using?



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[12345678]

Thanks for the reply. I didn't check it properly as I was in a rush to do the past paper so I missed that it was impossible!