You are Here: Home >< Maths

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
1. Find the ranges of values of k for which the equation

has roots of the same sign

My comment:
I understand that if a> 0 then k>0 and for f(x) to have roots

which leds to
but from the nature of the question I assume that it also considers distinct roots.

but I dont know how to get to that particular part of the solution.
from the book the answer is and

2. (Original post by bigmansouf)
Find the ranges of values of k for which the equation

has roots of the same sign

My comment:
I understand that if a> 0 then k>0 and for f(x) to have roots

which leds to
but from the nature of the question I assume that it also considers distinct roots.

but I dont know how to get to that particular part of the solution.
from the book the answer is and

these have the same sign when b>sqrt(b^2-4ac)>0 or b<-sqrt(b^2-4ac)<0
plug in the k things for b and c and 1 for a
3. (Original post by ValerieKR)

these have the same sign when b>sqrt(b^2-4ac)>0 or b<-sqrt(b^2-4ac)<0
plug in the k things for b and c and 1 for a
for part

then

for part
which will give the same result as above

Im very sorry but i am confused on what to do next. This is because from my view if k > 0, k> 1 and k > 9 according to edexcel math the answer is K > 9 which is not the answer given in the textbook

Also, how did you get the formula of
from ?

4. (Original post by bigmansouf)
for part

then

That k>1 should be a k<1 (sketch it and see where it's positive)

maybe you don't need the other one

they come from the fact that b+-sqrt(b^2-4ac)>0 or <0
and rearranging that in different ways
5. (Original post by ValerieKR)
That k>1 should be a k<1 (sketch it and see where it's positive)

maybe you don't need the other one

they come from the fact that b+-sqrt(b^2-4ac)>0 or <0
and rearranging that in different ways
yes you are right about the k > 1

please can i ask one more question i know its early in the morning?
6. (Original post by bigmansouf)
yes you are right about the k > 1

please can i ask one more question i know its early in the morning?
quick (yes of course you can any time)
7. (Original post by ValerieKR)
quick (yes of course you can any time)
rearranging
1) gives but from this how to i get to

do i just add > 0? is there a rule for this?

and same for rearranging
2) gives but from this how to i get to

sorry if this may be trivial but i self studying maths
8. (Original post by bigmansouf)
rearranging
1) gives but from this how to i get to

do i just add > 0? is there a rule for this?

and same for rearranging
2) gives but from this how to i get to

sorry if this may be trivial but i self studying maths
the square root sign makes whatever is inside positive so you need to add the <0 and >0 to avoid awkward scenarios
9. (Original post by ValerieKR)
the square root sign makes whatever is inside positive so you need to add the <0 and >0 to avoid awkward scenarios
thank you very much im truly sorry for the late reply
i cant rate you any more but thank a lot

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: September 15, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams