physics chemistry maths science forums
become expert I help I sign up I login
refer a friend - earn nickels!!   
 advanced
 
Home
Ask & Discuss Questions
Study Material
Experts Zone
Hang Out!

Ask & Discuss Questions with Community & Experts

 Moderation Team
 90 chars left    advanced
Ask iit jee aieee pet cbse icse state board community Community Discussion Question: quadratic..
Forum Index -> Algebra like the article? email it to a friend.  
Author Message
[Post New]24 Apr 2008 15:42:03 IST
    Subject: quadratic..
[Up] View Post
mathwiz (46)

Hot goIITian

Olaaa!! Perrrfect answer. 8  [11 rates]
mathwiz's Avatar
total posts: 161    
offline Offline
if a,b,c are the roots of x^3-3x^2+5x-7=0 then 1+ (1/ab) + (1/bc) +(1/ca)=?
    
[Post New]24 Apr 2008 15:52:19 IST
    Subject: Re:quadratic..
[Up] View Post
LAMPARD (1142)

Blazing goIITian

Olaaa!! Perrrfect answer. 190  [286 rates]
LAMPARD's Avatar
total posts: 777    
offline Offline
10/7???
MaNuTd RoXxXx..MaNuTd 2 WiN PrEmIeR LeAgUe ThIs SeAsOn ToO AlOnG WiTh ChAmPiOnS LeAgUe.....HaiL RoNaLdO ...HaiL LaMpArD...
 this reply: 2 points  (with 0 Olaaa!! Perrrfect answer.   in 1 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 15:57:56 IST
    Subject: quadratic..
[Up] View Post
mathwiz (46)

Hot goIITian

Olaaa!! Perrrfect answer. 8  [11 rates]
mathwiz's Avatar
total posts: 161    
offline Offline
give the method please..
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:04:40 IST
    Subject: Re:quadratic..
[Up] View Post
LAMPARD (1142)

Blazing goIITian

Olaaa!! Perrrfect answer. 190  [286 rates]
LAMPARD's Avatar
total posts: 777    
offline Offline
Is it correct??
MaNuTd RoXxXx..MaNuTd 2 WiN PrEmIeR LeAgUe ThIs SeAsOn ToO AlOnG WiTh ChAmPiOnS LeAgUe.....HaiL RoNaLdO ...HaiL LaMpArD...
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:08:40 IST
    Subject: quadratic..
[Up] View Post
mathwiz (46)

Hot goIITian

Olaaa!! Perrrfect answer. 8  [11 rates]
mathwiz's Avatar
total posts: 161    
offline Offline
i dono but its given in the option...so must be correct

but do u mind telling me how u did it???
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:15:20 IST
    Subject: Re:quadratic..
[Up] View Post
LAMPARD (1142)

Blazing goIITian

Olaaa!! Perrrfect answer. 190  [286 rates]
LAMPARD's Avatar
total posts: 777    
offline Offline
The expression can be written as
(abc+a+b+c)/abc
Now,abc is product of the roots which is 7
a+b+c is sum of the roots which is 3
Thus,the given exp. is equal to (7+3)/7  =10/7
MaNuTd RoXxXx..MaNuTd 2 WiN PrEmIeR LeAgUe ThIs SeAsOn ToO AlOnG WiTh ChAmPiOnS LeAgUe.....HaiL RoNaLdO ...HaiL LaMpArD...
 this reply: 2 points  (with 0 Olaaa!! Perrrfect answer.   in 1 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:20:34 IST
    Subject: quadratic..
[Up] View Post
mathwiz (46)

Hot goIITian

Olaaa!! Perrrfect answer. 8  [11 rates]
mathwiz's Avatar
total posts: 161    
offline Offline
i know to find the sum n product only for a second degree eq....

tell me how to find these for a 3rd degree eqn...
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:34:26 IST
    Subject: Re:quadratic..
[Up] View Post
LAMPARD (1142)

Blazing goIITian

Olaaa!! Perrrfect answer. 190  [286 rates]
LAMPARD's Avatar
total posts: 777    
offline Offline
ax3 +bx2+cx+d
-d/a is product of roots taken 3 at a time
c/a is product of roots taken 2 at a time
-b/a is sum of roots.
I'm not sure about the signs though.
MaNuTd RoXxXx..MaNuTd 2 WiN PrEmIeR LeAgUe ThIs SeAsOn ToO AlOnG WiTh ChAmPiOnS LeAgUe.....HaiL RoNaLdO ...HaiL LaMpArD...
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:34:45 IST
    Subject: Re:quadratic..
[Up] View Post
sboosy (2970)

Blazing goIITian

Olaaa!! Perrrfect answer. 522  [702 rates]
sboosy's Avatar
total posts: 498    
offline Offline
ax^3+bx^2+cx+d=0 \\ \\ \mbox{Let the roots of the equation be} \ \alpha,\beta,\gamma \\ \\ \mbox{Sum of the roots} = \frac{\mbox{-coeff.of} \ x^2}{\mbox{coeff.of} \ x^3} \Rightarrow \alpha+\beta+\gamma = \frac{-b}{a} \\ \\ \mbox{Sum taken two at a time} = \frac{\mbox{coeff.of} \ x}{\mbox{coeff.of} \ x^3} \ \Rightarrow \alpha\beta+\beta\gamma+\gamma\alpha = \frac{c}{a} \\ \\ \mbox{Product of the roots} \ = \frac{-\mbox{Constant term}}{\mbox{coeff.of} \ x^3} \ \Rightarrow \alpha\beta\gamma = \frac{-d}{a} \\
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:35:23 IST
    Subject: Re:quadratic..
[Up] View Post
pantpranav (306)

Scorching goIITian

Olaaa!! Perrrfect answer. 52  [75 rates]
pantpranav's Avatar
total posts: 233    
offline Offline
Let us consider an equation,
ax3 + bx2 + cx + d = 0
Then,
a+b+c+d = -b/a
ab+bc+ca = c/a
abc = -d/a


 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
[Post New]24 Apr 2008 16:45:37 IST
    Subject: quadratic..
[Up] View Post
mathwiz (46)

Hot goIITian

Olaaa!! Perrrfect answer. 8  [11 rates]
mathwiz's Avatar
total posts: 161    
offline Offline
thanks a lot ...lampard,sboosy,pantpranav...
 this reply: 0 points  (with 0 Olaaa!! Perrrfect answer.   in 0 votes )   [?]
 
You have to be logged on to rate
  
 
Forum Index -> Algebra
Go to:   

Top Offers for goIITians
Correspondence Courses
Brilliant Tutorials
Narayana Institute
Aakash Institute
Classroom/Crash Courses
Narayana - Kota , Delhi , Others
Brilliant Tutorials - Class , Crash
Aakash Institute - Medical , Engg
Online Test Series
Brilliant Tutorials
Narayana Institute
Aakash Institute
Mahesh Tutorials
AMITY      Sri Chaitanya