If x^2=x+1, then x^3=?
A. 3x+2
B. 3x-2
C. 2x+1
D. 2x-3
E. 3x+4
*An answer will be posted in 2 days.
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
If x^2=x+1, then x^3=?
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
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]
-
Humblejohny
- Newbie | Next Rank: 10 Posts
- Posts: 3
- Joined: Sat Aug 27, 2016 12:09 am
Ans C
given x^2 = x+ 1
bring to left x^2-x-1 = 0
multiply by x both sides, x(x^2-x-1)=0
x^3-x^2-x=0 --> x^3 = x^2+1, substitute x^2 value now we get x^3 = 2x+1
given x^2 = x+ 1
bring to left x^2-x-1 = 0
multiply by x both sides, x(x^2-x-1)=0
x^3-x^2-x=0 --> x^3 = x^2+1, substitute x^2 value now we get x^3 = 2x+1
-
MBA Challengers
- Senior | Next Rank: 100 Posts
- Posts: 51
- Joined: Fri Sep 09, 2016 11:59 pm
- Thanked: 20 times
Start with multiplying both sides by x.
Thus, x^3 = x^2 + x
Now, substitute the original value of x^2 in the equation above:
x^3 = (x + 1) + x
Thus, x ^ 3 = 2x + 1. The answer is C.
Thus, x^3 = x^2 + x
Now, substitute the original value of x^2 in the equation above:
x^3 = (x + 1) + x
Thus, x ^ 3 = 2x + 1. The answer is C.
Log on to www.mbachallengers.com for
Easy strategic GMAT prep
For any queries mail us at [email protected]
Follow MBA Challengers on Facebook
Easy strategic GMAT prep
For any queries mail us at [email protected]
Follow MBA Challengers on Facebook
-
GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Alternate approach:Max@Math Revolution wrote:If x^2=x+1, then x^3=?
A. 3x+2
B. 3x-2
C. 2x+1
D. 2x-3
E. 3x+4
x²=x+1 implies that the square of x is equal only to one more than x.
Thus, the roots of this equation must be very small.
If we test x=-1, x=-1/2, x=0, x=1/2 and x=1 in the given equation, the two sides are closest in value when x=-1/2.
Thus, one of the roots must be close to -1/2.
If x=-1/2, then x³ = -1/8.
Implication:
The correct answer choice must yield a value close to -1/8 when x=-1/2.
The value yielded by C is closest to -1/8:
2x+1 = (2)(-1/2) + 1 = 0.
The correct answer is C.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
