[GMAT math practice question]
What is (-1)*(-1)^2*(-1)^3* *...*(-1)^{2019}?
A. -2
B. -1
C. 0
D. 1
E. 2
What is (-1)*(-1)^2*(-1)^3* *…*(-1)^{2019}?
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]
- [email protected]
- Junior | Next Rank: 30 Posts
- Posts: 11
- Joined: Wed Oct 23, 2019 11:37 am
it's an easy one when you can really see what's being asked.
We have to ignore the numbers after the first number until the second last number.
Why?
Because for every even power of -1, there's an odd power, too.
Just look at the first number -1 and last -1 (raised to an odd power) = -1
-1*-1 = 1
answer D
We have to ignore the numbers after the first number until the second last number.
Why?
Because for every even power of -1, there's an odd power, too.
Just look at the first number -1 and last -1 (raised to an odd power) = -1
-1*-1 = 1
answer D
- 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
=>
Remember that 1 + 2 + 3 + ... + n = n(n+1)/2.
Since 1 + 2 + 3 + ... + 2019 = 2019*2020/2 = 2019*1010 and it is an even number, (-1)*(-1)^2*(-1)^3* *...*(-1)^{2019} = (-1)^{2019*1010} = 1
Therefore, D is the answer.
Answer: D
Remember that 1 + 2 + 3 + ... + n = n(n+1)/2.
Since 1 + 2 + 3 + ... + 2019 = 2019*2020/2 = 2019*1010 and it is an even number, (-1)*(-1)^2*(-1)^3* *...*(-1)^{2019} = (-1)^{2019*1010} = 1
Therefore, D is the answer.
Answer: D
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]