The Student Room Group

Discriminant

Basically Iv got 3 questions im stuck with different reasons :/. The first question x2 - 3x + 1 = 0 I used the discriminant and did -32 - 4x1x1 = 0
9 - 4 =5 is this right? this is a non calculator paper btw :smile:

The second question finding the value of a quadratic equation ax2+ 16x +32 = 0 I did the discriminant again and did 162 - 4 x 1 x 32 and got 256 - 128 = 128 i actually don't know if this is correct :/

And the 3rd question is find the values of K in the equation 2kx squared - x + 3 =0 has no real roots.

i have done -1 squared - 4x2x3 = - 23 which is below 0 meanign it has no roots. So 1 - 4x2x3 = 23
(edited 10 years ago)
Reply 1
Original post by ChocoholicCox
Basically Iv got 2 questions im stuck with with 2 different reasons :/. The first question x2 - 3x + 1 = 0 I used the discriminant and did -32 - 4x1x1 = 0
9 - 4 =5 is this right? this is a non calculator paper btw :smile:


The discriminant is 5, yeah. I don't know why you set those numbers equal to 0 though (bit in bold).

The second question finding the value of a quadratic equation ax2+ 16x +32 = 0 I did the discriminant again and did 162 - 4 x 1 x 32 and got 256 - 128 = 128 i actually don't know if this is correct :/

No, this time the discriminant is 256 - 128a - you can't just ignore the a.
Original post by Swayum
The discriminant is 5, yeah. I don't know why you set those numbers equal to 0 though (bit in bold).

oh right i don't know lol :wink:


No, this time the discriminant is 256 - 128a - you can't just ignore the a.

Oh if u do 256 - 128a what would the answer be :/?
Original post by ChocoholicCox
Oh if u do 256 - 128a what would the answer be :/?


Depends on what the question was asking.
Also in the third question you must not ignore k
Original post by brianeverit
Depends on what the question was asking.
Also in the third question you must not ignore k


Thanks Like you say with the 3rd question iv finished it and got -12 - 4 x 2 x 3 = -23 and got the answer no real roots because its below 0 but where do u put in the k thing lol
Original post by ChocoholicCox
Thanks Like you say with the 3rd question iv finished it and got -12 - 4 x 2 x 3 = -23 and got the answer no real roots because its below 0 but where do u put in the k thing lol


Discriminant should be 1โˆ’24k1-24k which will only be negative for certain values of k.
Original post by brianeverit
Discriminant should be 1โˆ’24k1-24k which will only be negative for certain values of k.


oh right yeah thx i see i made a few mistakes :colondollar:
Reply 7
Original post by ChocoholicCox
oh right yeah thx i see i made a few mistakes :colondollar:


You do not seem to have any idea what the purpose of the discriminant is

Also, you are not understanding aha the questions are asking

If you understood this topic at all you would realise that we need to know what the question is


I suggest that you see your teacher and ask them to go through the whole topic with you from the start
Original post by TenOfThem
You do not seem to have any idea what the purpose of the discriminant is

Also, you are not understanding aha the questions are asking

If you understood this topic at all you would realise that we need to know what the question is


I suggest that you see your teacher and ask them to go through the whole topic with you from the start


Yeha sure thx tbh all i know is that it is used for something well no root = below 0, equal to zero means 1 root and 2 roots above 0 :P, shortened version of the quadratic formula and know it of by heart b2 - 4ac :colone:
(edited 10 years ago)
Reply 9
Original post by ChocoholicCox
Yeha sure thx tbh all i know is that it is used for something, shortened version of the quadratic formula and know it of by heart b2 - 4ac :colone:


Yeah, I can see that you have a vague understanding ... but if a student of mine were floundering as you seem to be I would want to know so that I could do a full explanation
Original post by TenOfThem
Yeah, I can see that you have a vague understanding ... but if a student of mine were floundering as you seem to be I would want to know so that I could do a full explanation


thanks :smile: Yeah i will ask my teacher but the last time I told my teacher before about another subject which was polynomials ( didn't learn anything from the revision session) he said oh come see me at Wednesday Lunchtime (45 mins long) i had the first 2 periods then i had the whole day of but had to wait 2 hours 30 mins till lunch to see him i did appear at lunchtime then he went through with me in like 5 mins and was just like oh we will do it in short periods and i was just like WTf i told him i had waited 2 hours 30 mins and he laughed and it was ironic because once he said we should do it in short periods because his smoker buddy walked past to go outside :/ hes a smoke addict and spends his lunch and break times doing that so yeah basically he couldn't give care :frown:
(edited 10 years ago)

Quick Reply

Latest