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# C1 quadratic inequality question watch

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

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