BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Discriminant

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
Legendary Member
Posts: 1084
Joined: Fri Apr 15, 2011 2:33 pm
Thanked: 158 times
Followed by:21 members

by pemdas » Sun Feb 26, 2012 9:57 am
knight247 wrote:I'm hoping to get a purely algebraic approach to this one. Preferably using discriminant if possible.
OA is 42
can help with algebraic approach, yet discriminant solution is tedious

I am using FOIL for p^2-kp-28=0
possible solutions (p-28)(p+1)=0, (p-14)(p+2)=0, (p-7)(p+4)=0
in all solutions we get the value -28 for independent argument (C) and different values for k such as -28+1=-27, -14+2=-12, -7+4=-3. Since k is positive and our quadratics contains -1*k we obtain the sum of all possible values for k as 27+2+3=42
Success doesn't come overnight!
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 425
Joined: Wed Dec 08, 2010 9:00 am
Thanked: 56 times
Followed by:7 members
GMAT Score:690

by LalaB » Sun Feb 26, 2012 10:57 am
p^2-kp-28=0

using Vieta's theorem (https://en.wikipedia.org/wiki/Vieta%27s_formulas)

p1*p2=-28
p1+p2=-(-k)

p1 p2 can be (28; -1) ; (14;-2); (7;-4)

28-1+14-2+7-4=42

p.s. I forgot this formula, but few days ago I did math of my nephew, and was pleased to see such a useful theorem )))) verdict- sometimes it is good to help kids )))
Happy are those who dream dreams and are ready to pay the price to make them come true.(c)

In order to succeed, your desire for success should be greater than your fear of failure.(c)
Top
Legendary Member
Posts: 1084
Joined: Fri Apr 15, 2011 2:33 pm
Thanked: 158 times
Followed by:21 members

by pemdas » Sun Feb 26, 2012 12:40 pm
@knight, why in your post you seek discriminant solution? Is this something related to graphical solution of equation?
Success doesn't come overnight!
Top
Post new topic Post Reply
• Page 1 of 1