Onequality with pronumeral at the bottom (1 Viewer)

[petergriffin198]

Guys this confuses me... If theres a p on the bottom dont u have to times both sides by p swuared this is from ruse 2012 question 11

 

[Drsoccerball]

It's because both p's cancelled if it had a value it would of popped up in the inequality but it doesn't therefore no solution.

 

[Speed6]

No, its simple algebra, if you want to get rid of the p on the denominator you must multiply b.s by p, hence cancelling the p in the denominator in the R.H.S.

IF there was a in the denominator, then yes, you will multiply throughout and then you will be left with a quadratic to solve.

 

[petergriffin198]

Yea but when u are aolving an inqequality with p on bottom how come they just cross multiplied.. I thought u cant do that in that u have to times both sides by p squared

 

[petergriffin198]

Eg
1/x + 5 < 1

U cant just times both sides by (x + 5) can u

 

[Speed6]

Yea but when u are aolving an inqequality with p on bottom how come they just cross multiplied.. I thought u cant do that in that u have to times both sides by p squared

They didn't, they just multiplied throughout (they should of indicated that they did that for the marker to see, however it is not warranted).

 

[InteGrand]

Guys this confuses me... If theres a p on the bottom dont u have to times both sides by p swuared this is from ruse 2012 question 11

Possibly the p is known to be positive from the question (is it a probability or something)? If so, we can just multiply through by p.

 

[petergriffin198]

Ok how bout my example with x + 5 on the bottom?

 

[InteGrand]

(Yes, in general we can't just multiply through by a variable since the variable could be negative, and that would flip the inequality.)

 

[petergriffin198]

They didn't, they just multiplied throughout (they should of indicated that they did that for the marker to see, however it is not warranted).

Oh ok thx yea ot says positive

 

[Drsoccerball]

Yea but when u are aolving an inqequality with p on bottom how come they just cross multiplied.. I thought u cant do that in that u have to times both sides by p squared

We know p is positive since is a probability.
Edit: beaten above

 

[Speed6]

Eg
1/x + 5 < 1

U cant just times both sides by (x + 5) can u

Yes you can! You must get rid of the in the denominator





i.e

 

[petergriffin198]

(Yes, in general we can't just multiply through by a variable since the variable could be negative, and that would flip the inequality.)

U besst... Thx

 

[InteGrand]

Ok how bout my example with x + 5 on the bottom?

1/(x+5)

 

[petergriffin198]

Thx boys fot it

 

[InteGrand]

Yes you can! You must get rid of the in the denominator





i.e

We can only do this if x + 5 > 0. For the case where x + 5 < 0, we must flip the inequality sign, since multiplying through by a negative number flips inequality signs.

 

[Speed6]

Yep sorry, my bad, that is correct.