maths p3 - deciding range of inequality after solving it

[Mortal9090]

hi,

look at question 1 nov 2010 - p3..

its ok to square both of the sites and solve like quadratic equation..

i get answers of x=1 and x=-7

now who do i decide the range?

 

[intel1993]

i want to ask the same thing plzz help anyone?????

 

[ahmed t]

well if u got ur quadratic ax^2+bx +c<0 then it will be inbetween
but if it is more than it will be greater than the larger one and smaller than the smaller one

remember if u start off with a modulus on one side and a linear on the other side
like this Ix+2I>x-5
then u must check your ansers as one of the inequalities might be wrong

 

[jejunestar]

hi,

look at question 1 nov 2010 - p3..

its ok to square both of the sites and solve like quadratic equation..

i get answers of x=1 and x=-7

now who do i decide the range?

when using quadratic equation formula on inequalities don't use "equals to sign" ("= ") use the sign assigned in the inequality for example for the inequality
5x^2 +30x -35 < 0,
the answer using quadratic equation must be written as x < 1 and x > -7 not x= 1 and x= 7
for the sign interchange,
when you take positive value the sign remains same
For example if x < (-30 ± 40)/10 when you take the positive value x < (-30+40)/40
and when taking the negative value, the sign is changed thus, x > (-30-40)/40
thus x < 1 and x > -7
hope this helps