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3:25 PM
@LeakyNun Done.
How do I make Chemistry.SE as my main site @LeakyNun?
 
@Abcd from which account?
 
@LeakyNun From this one, till the time I earn sufficient reputation from my new account.
 
but you deleted your account
 
@LeakyNun I didn't delete Chemistry.SE account. I deleted maths.SE and others.SE
 
3:30 PM
If $alpha$ and $\beta$ are the roots of the equation $ax^2+bx+c= 0$ express the roots of the equation $a^3x^2-ab^2x+b^2c=0$ in terms of $\alpha$ and $\beta$ @LeakyNun. I have the solution. I have a doubt in one part of it.
 
what is your doubt?
 
The solution is:
Divide by b^2
Finally, $\dfrac{-a}{b}x= \alpha$ or $ \beta$./ How @LeakyNun?( I arrived at the equation: a(-ax/b)^2 + b(-a/bx)+c = 0
if you want the intermediate steps let me know.
 
I don't understand "$\alpha$ or $\beta$".
 
Now how is that term equal to alpha or beta
@LeakyNun $\dfrac{-a}{b}x$ is equal to either alpha or beta.
Is it still unclear @LeakyNun?
 
I get it now
let u = -ax/b
 
3:36 PM
@LeakyNun ok
 
then you arrive at au^2 + bu + c = 0
so u = alpha or beta
-ax/b = alpha or beta
 
@LeakyNun please tell me one concrete application of Quadratic equations and the problems we solve in real life. It would be okay if you answer in a single line concisely.
 
@Abcd no idea.
 
@LeakyNun np
 
3:57 PM
@LeakyNun Why is quadratic function f(x)'s (of form $y = f(x)= ax^2+bx+c$) graph always upward parabola when a is positive?
It's just given in my book without any reason.
 
define parabola
what is it that you are asking
why it is shaped like a parabola or why it is upward?
 
@LeakyNun A parabola is a conic section whose distance from focus and directrix is always constant.
 
@Abcd no that's a circle
 
@LeakyNun I don't know the answer to either of those two questions.
 
have you learnt graph transformation?
 
4:00 PM
@LeakyNun No.
 
@Abcd are you supposed to have learnt it?
 
@LeakyNun No. I think we will be taught that in 12th/
 
do you know complete the square?
 
@LeakyNun What is that?
 
4:03 PM
@LeakyNun Yes, I know this
7 mins ago, by Abcd
@LeakyNun Why is quadratic function f(x)'s (of form $y = f(x)= ax^2+bx+c$) graph always upward parabola when a is positive?
 
so it can be expressed as $a(x-h)^2+k$ right?
 
@LeakyNun Why are a, h and k necessary?
 
@Abcd "so it can be expressed as $(x-1)^2+4$ right?" doesn't look good
 
@LeakyNun Yes.
 
what
I thought you were talking about general quadratic equations
 
4:10 PM
@LeakyNun So? I am talking about quadratics in x.
 
so we need those variables.
well then why do you need a, b, and c?
 
@LeakyNun okay
@LeakyNun understood.
@LeakyNun yes
 
I don't know how I should go on if you don't know function transformation
 
@LeakyNun So you can't explain why it's a parabola and why the curve is upwards? If that's the case, I will simply learn that info unfortunately.
 
I can't
 
4:16 PM
Could you explain why function is always positive if Discriminant is negative and coefficient of x is positiv?
 
discriminant is negative means that it doesn't touch the x-axis
 
@LeakyNun Yes
 
so it's either always positive or always negative
 
yes, then?
 
as x grows large, x^2 becomes much bigger than x, so the sign of the coefficient of x^2 dominates
 
4:17 PM
@LeakyNun What about constant c?What if it's really really really large or small?
 
@Abcd x can always become larger
x can always be really really really larger
 
@LeakyNun That wasn't a condition.
@LeakyNun but I took c as larger in magnitude but opposite sign. then?
 
c is fixed.
 
@LeakyNun yes
 
then I make x twice as large :P
 
4:19 PM
@LeakyNun What about x being 1 and c being -1000000000000000. Won't parabola move downwards?
 
x isn't fixed.
@Abcd the parabola is fixed
it can't "move"
your assumption is that it doesn't touch the x-axis
 
@LeakyNun How confusing.
 
@Abcd what
 
@LeakyNun Okay, understood.
 
lol
 
4:23 PM
@LeakyNun What is the effect of c on the parabola?
 
y-intercept
 
4:40 PM
@LeakyNun Please help me simplify $0<a^2-4b<c^2$
 
what do you mean by simplify?
 
@LeakyNun To reduce it to $\dfrac{(a^2-c^2)}{4}<b< \dfrac{a^2}{4}$
@LeakyNun Just out of curiosity: what does d in \dfrac stand for?
 
@Abcd \displaystyle
$0<a^2-4b<c^2$
$-a^2<-4b<c^2-a^2$
$a^2>4b>a^2-c^2$
$\dfrac{a^2}4>b>\dfrac{a^2-c^2}4$
 
Okay :)
$(x-a)(x-12)+13 = 0$ Why is it necessary for $a$ and other coefficients to be rational for the equation to have integral roots? I mean I was told this condition but I can't interpret it's reason @LeakyNun.
@LeakyNun Really sorry for asking so many basic questions :"(. Today I was even scolded by my teacher for asking too many doubts during the class :"(.
 
4:55 PM
because if $x$ is an integer, then so is $x-12$, and if $a$ is irrational then $x-a$ is irrational
(x-a)(x-12) becomes irrational times rational
unless x=12, we must obtain irrational
and then +13 gives you also irrational
 
What are other conditions for that equation to have integral roots @LeakyNun?
 
$\Delta = (a+12)^2 - 624a$ be a perfect square
@Abcd because you need to take its square root in the quadratic formula
 
@LeakyNun Yes, right.
@LeakyNun Anymore conditions?
 
@Abcd no, that's not it
just solve the goddam equation to see if it has integral roots
 
@LeakyNun I just need the integral value of $a$ in that question for the equation to have integral roots
 
5:06 PM
@Abcd ?
who gave you that question?
$(a-x)(x-12)=13$
$a-x = \dfrac{13}{x-12}$
$a=x+\dfrac{13}{x-12}$
 
@LeakyNun then?
 
so just check whether $a$ is in that form.
I can't provide you with any further characterisation
 
@LeakyNun No it's not. There are values given of a as -2 or 26
 
what
then why don't you just list them out
so you want $a$ to be integer
then $x-12$ must divide $13$
 
@LeakyNun Yes,.
 
5:12 PM
@Abcd then why the hell did you not state it earlier
stop leading me in circles
 
@LeakyNun And x = root of equation should also be a integer
@LeakyNun I said that
 
@Abcd so how many divisors does $13$ have?
 
6 mins ago, by Abcd
@LeakyNun I just need the integral value of $a$ in that question for the equation to have integral roots
@LeakyNun integral ^
 
you edited it twice
 
@LeakyNun still really sorry for not being absolutely clear.
@LeakyNun I will type carefully from now on. Promise.
 
5:14 PM
1 min ago, by Leaky Nun
@Abcd so how many divisors does $13$ have?
 
@LeakyNun Only 13 and 1
 
@Abcd and negative numbers?
 
@LeakyNun -13 and -1
 
so possible values of $x$?
 
@LeakyNun 13, -1, 1?
 
5:17 PM
@Abcd no
4 mins ago, by Leaky Nun
then $x-12$ must divide $13$
 
@LeakyNun 13 and -1
 
@Abcd why?
when did I say that $x$ must divide $13$?
 
@LeakyNun 13-12 and -1 -12 divide 13 to yield integers
 
x-12 is a divisor of 13
x-12 can be -13 -1 1 13
so what can x be?
 
@LeakyNun x can be -1 , 11, 13, 25
 
5:20 PM
13 mins ago, by Leaky Nun
$a=x+\dfrac{13}{x-12}$
then what can $a$ be?
 
@LeakyNun -2 and 26 :)
Your method is best @LeakyNun. Teacher had given a really long method for this.
 
no problem
 
5:35 PM
@LeakyNun What does cyclic coefficients mean?
 
@Abcd where do you see that?
 
@LeakyNun $(a+2b-3c)x^2 + (b+2c-3a)x + (c+2a-3b)=0$ is an equation given as a part of a question. SOlution begins with "as coefficients are cyclic, f(1) = 0"
solution*
 
it means, well, the one is just the other with the names changed in a cyclic fashion
 
@LeakyNun What do you mean?
 
if you consider $a+2b-3c$
and then change each variable to the next
wrapping $c$ back to $a$
then you get $b+2c-3a$
 
5:39 PM
@LeakyNun Got it.
 
5:53 PM
What can we conclude if coefficient of x is positive and D is positive @LeakyNun?
 
@Abcd then it intersects the x-axis at two place and opens upward
 
@LeakyNun why does it open upwards?
 
wait, coefficient of what is positive?
 
@LeakyNun $x^2$ :"(
4 mins ago, by Abcd
What can we conclude if coefficient of x is positive and D is positive @LeakyNun?
x^2*
My teacher says x and implies x^2 so I just got that habit. Sorry.
 
so it opens upward because the coefficient of $x^2$ is positive
 
6:07 PM
`prove that the set of values of k for which $18x^2 -6(2k+1) +k(k+1)= 0$ may have one root less than k and othe root greater than k are given by $(0,\frac{5}{7})$
I got $\Delta = 72k^2 +72k +36$ = always positive @LeakyNun (therfore 2 real and distinct roots exist)
What to do next?
therefore*
2 mins ago, by Abcd
`prove that the set of values of k for which $18x^2 -6(2k+1) +k(k+1)= 0$ may have one root less than k and othe root greater than k are given by $(0,\frac{5}{7})$
$18x^2- 6(2k+1)x +k(k+1)= 0$
:39796151 A long circular bracket is given. The one that indicates open interval.
 
right
if you want one root less than k and other root greater than k
let $f(x) = 18x^2-6(2k+1)x+k(k+1)$
then you want $f(x+k)=0$ to have a positive root and a negative root
 
@LeakyNun ok
@LeakyNun DIdn't get this
 
if x is less than k then x-k is negative
if x is greater than k then x-k is positive
let u=x-k
then we want f(x) = f(u+k) = 0 to have a positive root and negative root for u
 
@LeakyNun why not x+k
 
@Abcd we want u=x-k to be negative and positive
 
6:17 PM
@LeakyNun I am still a little confused. Any simpler explanation?
 
3 mins ago, by Leaky Nun
if x is less than k then x-k is negative
x<k
x-k<0
 
@LeakyNun What is x here? Root of the equation?
Is x only the root of the equation @LeakyNun?
 
the root of the equation
?
 
@LeakyNun After finding Discriminant, solution finds f(k) = 7k^2- 5k = k(7k-5)<0
 
oh, right
that's better
 
6:30 PM
@LeakyNun Could you explain what the solution has tried to do?
 
since $f(x)$ is an upward parabola
 
@LeakyNun yes
 
it hits the x-axis once before $k$ and once after $k$
 
@LeakyNun yes
 
so it must be negative between
 
6:32 PM
@LeakyNun yes, then?
 
so $f(k)<0$
 
Understood @LeakyNun :)
How to elaborate $7k^2-5k <0$ @LeakyNun?
 
k(7k-5) < 0
0 < k < 5/7
(consider the roots of k(7k-5))
 
@LeakyNun Got it :)
 
6:49 PM
I made two cases. What to do next?
Consider the inequation $x^2 +|x+a|-9<0$. Find the values of the real parameter a so that the given inequation has at least one negative solution @LeakyNun.
$a$
 
$0 \le |x+a| < 9-x^2$
$x^2-9<0$
$-3<x<3$
 
@LeakyNun How?
 
@Abcd from the line immediately above
 
@LeakyNun okay, then?
 
@Abcd thinking
 
6:59 PM
@LeakyNun still?
 
@Abcd yes
$|x+a|<9-x^2$
$x^2-9<x+a<9-x^2$
$x^2-x-9<a<-x^2-x+9$
 
Why did you remove those? They were correct.
 
@Abcd but they weren't fruitful
 
@LeakyNun How?
 
@Abcd $|a|<b \implies -b<a<b$
 
7:07 PM
@LeakyNun Please derive this.
 
$a^2<b^2$
$(a-b)(a+b)<0$
$-b<a<b$
 
@LeakyNun Okay, next?
 
5 mins ago, by Leaky Nun
$x^2-x-9<a<-x^2-x+9$
 
@LeakyNun then?
@LeakyNun Solution does it this way: case 1; Let x+a>0 $\implies$ For all $x<0, a>|x|$ Also, $x^2 + x+a -9 <0$
 
we proceed to maximize $-x^2-x+9$ and minimize $x^2-x-9$
 
7:13 PM
i.e. 0< a<37/4. Then solution does similar stuff for Case II
 
$-x^2-x+9=-(x+0.5)^2+9.25$
$x^2-x-9 = (x-0.5)^2 -9.25$
the maximum of $-x^2-x+9$ thus occurs when $x=-0.5$, where it is $9.25$
the minimum of $x^2-x-9$ when $-3<x\le0$, however, occurs when $x=0$, where it is $-9$
 
@LeakyNun Didn't get you
 
we thus conclude $-9 < a < 9.25$
9 mins ago, by Leaky Nun
$x^2-x-9<a<-x^2-x+9$
 
@LeakyNun What do you mean?
@LeakyNun Correct answer
 
$\underbrace{x^2-x-9}_{\text{minimize}}<a<\underbrace{-x^2-x+9}_{\text{maximize}‌​}$
 
7:15 PM
@LeakyNun why minimise it and maximise the other?
 
we want to find what $a$ can be
 
so?
 
so we find that $-9<x^2-x-9<a<-x^2-x+9<9.25$
which is done by maximizing the latter and minimizing the former
so $-9<a<9.25$
 
Please explain in simpler terms @LeakyNun/
 
@Abcd use desmos
 
7:19 PM
@LeakyNun what about the part "the given inequation has at least one negative solution"
 
@Abcd it means there is $x<0$ that satisfies the inequality
 
@LeakyNun I can't understand your solution at all.
 
$a$ is bounded between the blue curve and the red curve
 
7:32 PM
@LeakyNun I tried hard to understand but in vain :/
@LeakyNun Can you explain step by step, slowly?
 
28 mins ago, by Leaky Nun
$x^2-x-9<a<-x^2-x+9$
 
@LeakyNun agreed
 
so $a$ is between that two curves
 
@LeakyNun Yes
 
and we want to find out what $a$ can be
 
7:36 PM
@LeakyNun But there's another constraint in the question too. How can we avoid that?
 
@Abcd what constraint?
 
@LeakyNun "so that the given inequation has atleast one negative solution"
 
17 mins ago, by Leaky Nun
@Abcd it means there is $x<0$ that satisfies the inequality
23 mins ago, by Leaky Nun
the minimum of $x^2-x-9$ when $-3<x\le0$, however, occurs when $x=0$, where it is $-9$
I already took care of it here
 
@LeakyNun So we will check this in the end?
 
31 secs ago, by Leaky Nun
I already took care of it here
 
7:40 PM
@LeakyNun x<0 not <=
 
@Abcd so it won't reach $-9$
 
@LeakyNun What about the a? I am confused as hell especially because of two variables
 
@Abcd the $a$ is always greater than $x^2-x-9$
 
@LeakyNun See solution's method:
case 1: Let x+a>0 $\implies $ for all x<0 ,. $a>|x|$ Also, $x^2+x+a-9<0 \implies a<9-x^2-x$
$\implies 0<a< \dfrac{37}{4}$
Case II
let x+a<0 $\implies$ for all x<0, a<|x|
Also,$ x^2-x-a-9<0$
Thus, -9<a<37/4 (I skipped typing a step)
can you explain solution's method @LeakyNun?
 
tell me where you do not understand
 
7:49 PM
@LeakyNun For all x<0, a>|x| part
 
x is negative
yet x+a>0
so a has to be more positive than x is negative
 
right
 
so a>|x|
 
@LeakyNun does solution use this result again anywhere for verification or something?
 
@LeakyNun use what?
 
7:52 PM
@LeakyNun Yes. Does solution use the two results anywhere?
 
what result?
 
or are they just for display
@LeakyNun a>|x|. What is it's use?
 
well, a>|x|>0
 
@LeakyNun why not mod of a also i.e. why not |a|> |x|?
 
@Abcd it doesn't matter
a is positive anyway
 
7:57 PM
How did solution jump from $a>x^2-x-9$ to $a>9$ @LeakyNun?
In second case..
 
43 mins ago, by Leaky Nun
the minimum of $x^2-x-9$ when $-3<x\le0$, however, occurs when $x=0$, where it is $-9$
 
1 hour on a question ! I am dead :"( :( :( :"( . I am leaving this question @LeakyNun.
 
ok
 
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