Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 04 May 2015, 18:21

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Find the value of 'b' if sqrt7 is a root of the equation x^2

Author Message
TAGS:
Senior Manager
Joined: 30 Aug 2003
Posts: 330
Location: BACARDIVILLE
Followers: 1

Kudos [?]: 1 [0], given: 0

Find the value of 'b' if sqrt7 is a root of the equation x^2 [#permalink]  30 Jan 2004, 15:20
Find the value of 'b' if sqrt7 is a root of the equation x^2 + ax - 14 = 0 and the equation x^2 + ax + b = 0 has real and equal roots.

7/4
-7/4
49/4

none of these
_________________

Pls include reasoning along with all answer posts.
****GMAT Loco****
Este examen me conduce jodiendo loco

Manager
Joined: 25 Jan 2004
Posts: 92
Location: China
Followers: 1

Kudos [?]: 2 [0], given: 0

from the second eqn: equal and real roots
a^2 = 4b

from the first eqn, let k be the other root

sqrt(7)+ k = - a
ksqrt(7) = -14

Thus b = (1/4)[sqrt(7) - [14/sqrt(7)]]^2

Last edited by Zhung Gazi on 30 Jan 2004, 16:12, edited 1 time in total.
Senior Manager
Joined: 30 Aug 2003
Posts: 330
Location: BACARDIVILLE
Followers: 1

Kudos [?]: 1 [0], given: 0

Rakesh, we did a similar problem yesterday, but I am having problems with this question. Can u help
_________________

Pls include reasoning along with all answer posts.
****GMAT Loco****
Este examen me conduce jodiendo loco

Manager
Joined: 26 Dec 2003
Posts: 227
Location: India
Followers: 1

Kudos [?]: 2 [0], given: 0

Yeah ur posting such wonderful avathars. We go step by step

from the first eq. let p & q be the roots then we know that p+q= - b/a (the eq is of the form ax^2 + bx +c ), so p+q = -a/1 = -a ( eq is x^2+ax-14) and pq = c/a = -14, we are given that one root is sqrt7 then let p=sqrt7 , we know that pq=-14, so (sqrt7* q) = -14 solve and we get q = -2sqrt7, we also know that p =sqrt7 and p+q = -a, substitute the values of p & q and we get a=sqrt7----------------(1)

from the second eq, we r given that it has real and equal roots so it means b^2- 4ac=0 ( for eq of the form ax^2 +bx +c) so as the given eq is of the form x^2 +ax+b=0 , we get a^2 - 4 * 1 * b=0, so a^2=4b, we know that a=sqrt7 ( from -----(1) above) substitute this value of a in a^2=4b and we get b=7/4.
Senior Manager
Joined: 30 Aug 2003
Posts: 330
Location: BACARDIVILLE
Followers: 1

Kudos [?]: 1 [0], given: 0

_________________

Pls include reasoning along with all answer posts.
****GMAT Loco****
Este examen me conduce jodiendo loco

Similar topics Replies Last post
Similar
Topics:
Find a possible value of a+b given the equations 1 03 Jan 2013, 03:36
3 If there is exactly one root of the equation x^2 + ax + b 8 03 Mar 2012, 17:14
If there is exactly one root of the equation x^2 + ax + b 8 23 Aug 2011, 22:17
What are the unique values of b and c in the equation 4x^2 + 2 27 Oct 2010, 11:12
If equation x^2+bx+c=0 have two same roots, b=? (1) c=9 (2) 2 21 Jun 2008, 18:16
Display posts from previous: Sort by