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

Redeem

Cross Multiplication

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Senior | Next Rank: 100 Posts
Posts: 42
Joined: Tue Dec 20, 2011 6:26 pm
Thanked: 2 times
Followed by:1 members

Cross Multiplication

by dlencz » Sun May 13, 2012 3:46 pm
Could someone explain how you get from the first line to the second line or a good resource for understanding cross multiplication a little better? Thanks.
Image
Top
Source: — Data Sufficiency |
User avatar
Legendary Member
Posts: 520
Joined: Sat Apr 28, 2012 9:12 pm
Thanked: 339 times
Followed by:49 members
GMAT Score:770

by eagleeye » Sun May 13, 2012 5:50 pm
Hi dlencz:

To go from first line to the second, you have to multiply both the left and right hand side by the product of the denominators of the two sides. One can only do this when the product of the two is positive which means it is greater than 0. You can always do this without changing the sign, as long as the the factor you are multiplying both sides with is > 0. Luckily, in this case (b-k)(b+k)>0 is given.

Thing to watch
If the product was negative i.e. if (b-k)(b+k) < 0, then the inequality changes sign.
Top
Post new topic Post Reply
• Page 1 of 1