[GMAT math practice question]
x^3-y^3 = 9 and x-y = 3. What is the value of xy?
A. -2
B. -1
C. 0
D. 1
E. 2
x^3-y^3 = 9 and x-y = 3. What is the value of xy?
This topic has expert replies
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]
- Max@Math Revolution
- Elite Legendary Member
- Posts: 3991
- Joined: Fri Jul 24, 2015 2:28 am
- Location: Las Vegas, USA
- Thanked: 19 times
- Followed by:37 members
=>
x^3-y^3 = (x-y)(x^2+xy+y^2) = 3(x^2+xy+y^2) = 9
Therefore, x^2+xy+y^2 = 3.
Now,
x^2+xy+y^2 = (x-y)^2 + 3xy = 3^2 + 3xy = 9 + 3xy = 3.
So,
3xy = -6
and xy = -2.
Therefore, the answer is A.
Answer: A
x^3-y^3 = (x-y)(x^2+xy+y^2) = 3(x^2+xy+y^2) = 9
Therefore, x^2+xy+y^2 = 3.
Now,
x^2+xy+y^2 = (x-y)^2 + 3xy = 3^2 + 3xy = 9 + 3xy = 3.
So,
3xy = -6
and xy = -2.
Therefore, the answer is A.
Answer: A
Math Revolution
The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online.
Email to : [email protected]