GRE Prep 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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
If x + y = –3 and x2 + y2 = 12, what is the value of 2xy?
[#permalink]
23 Jun 2018, 11:49
23 Jun 2018, 11:49
Expert Reply
4
Bookmarks
00:00
Question Stats:
87% (00:44) correct
12% (01:55) wrong based on 55 sessions
Hide Show timer Statistics
Re: If x + y = –3 and x2 + y2 = 12, what is the value of 2xy?
[#permalink]
25 Jun 2018, 07:03
25 Jun 2018, 07:03
Ans. -3
Re: If x + y = –3 and x2 + y2 = 12, what is the value of 2xy?
[#permalink]
28 Jul 2018, 16:07
28 Jul 2018, 16:07
1
Expert Reply
Explanation
One of the “special products” you need to memorize for the GRE is \(x^2 + 2xy + y^2 = (x + y)^2\).
Write this pattern on your paper, plug in the given values, and simplify, solving for 2xy:
\(x^2 + 2xy + y^2 = (x + y)^2\)
\((x^2 + y^2) + 2xy = (x + y)^2\)
\((12) + 2xy = (–3)^2\)
\(12 + 2xy = 9\)
\(2xy = –3\)
One of the “special products” you need to memorize for the GRE is \(x^2 + 2xy + y^2 = (x + y)^2\).
Write this pattern on your paper, plug in the given values, and simplify, solving for 2xy:
\(x^2 + 2xy + y^2 = (x + y)^2\)
\((x^2 + y^2) + 2xy = (x + y)^2\)
\((12) + 2xy = (–3)^2\)
\(12 + 2xy = 9\)
\(2xy = –3\)
