If m and n are non-zero integers, is m6-m5-m4 divisible by n? 1) m2

Question

If m and n are non-zero integers, is  m^6-m^5-m^4  divisible by n?

1)  m^2-1=m+n^2 
2)  m^4-2m^3+m^2=n^2+11

origen87 · Answer

m and n can either be positive or negative.
When m is negative
m^6+m^5-m^4. m4(m2+m-1)
When m is positive
m4(m2-m-1)
1) m2-m-1=n2
Divisible when m is negative but not when m is positive.
2)m2(m2-2m+1)=n2+11
Insuff.

IMO E

Please post the solution

BillyZ · Answer

OFFICIAL SOLUTION

If you modify the original condition and the question, m^6-m^5-m^4 = nt ? (t = any non-zero integer), so you get  m^4(m^2-m-1)=nt ?. If you look at con 1), from  m^2-m-1=n^2 , if you substitute it to  m^4(m^2-m-1) , you get  m^4(m^2-m-1)=m^4*n^2=n(m^4n) , hence yes, it is sufficient. For con 2), it is difficult to approach the question, but if you apply CMT 4 (B: if you get A or B too easily, consider D), it is also sufficient. Therefore, the answer is D. If you actually solve it, for con 2), you get  (m^2)^2-2m(m^2)+m^2=(m^2-m)^2=n^2+11 ,  (m^2-m)^2-n^2=(m^2-m-n)(m^2-m+n)=11 ,

① When it becomes m^2-m-n=1 and m^2-m+n=11, from m^2-m-n=1, you get m^2-m-1=n, so m^4(m^2-m-1)=m^4*n, hence yes.

② When it becomes m2-m-n=11 and m^2-m+n=1, if you add the two equations, you get 2(m^2-m)=12, m^2-m=6 and n=-5, then m^2-m-1=6-1=5=(-1)(-5)=-n, so from m^4(m^2-m-1)=m^4(-n), it is also yes.

③ When it becomes m^2-m-n=-1 and m^2-m+n=-11, if you add the two equations, from 2(m^2-m)=-12, m^2-m=-6 and n=-5, integer m that satisfies this does not exist, so it is out of scope.

④ When it becomes m^2-m-n=-11 and m^2-m+n=-1, if you add the two equations, from 2(m^2-m)=-12, m^2-m=-6 and n=5, integer m that satisfies this does not exist, so it is out of scope.

Therefore, as ①, ② shown above, it always becomes yes, hence it is sufficient. Therefore, the answer is D.

warrior1991 · Answer

Bunuel   chetan2u   VeritasKarishma  Please help on solving St:2

KarishmaB · Answer

m and n are non negative integers.

Ques: Is (m^6 - m^5 - m^4) divisible by n?

Stmnt 2: 
 m^2(m^2-2m+1)=n^2+11 
 m^2 (m - 1)^2 = n^2 + 11

Now note that LHS is a perfect square so RHS must be a perfect square too. n is an integer and its square is n^2. 
n^2 + 11 needs to be a perfect square too. Two consecutive perfect squares with a difference of only 11 between them must be 25 and 36 (the difference between consecutive perfect squares keeps increasing) 
So n must be 5 so that n^2 + 11 is 36 which is also a perfect square.

m^2 (m - 1)^2 = 36 
 (m(m-1))^2 = 6^2 
 m*(m-1) = 6 
m = 2

We have the values for both m and n so we can find whether the given expression is divisible by n. 
Sufficient.

Kinshook · Answer

Asked: If m and n are non-zero integers, is  m^6-m^5-m^4  divisible by n?

1)  m^2-1=m+n^2 
 m^2 - m - 1 = n^2 
 m^4(m^2 - m - 1) = m^4*n^2 
 m^6-m^5-m^4 = m^4*n^2 
 m^6-m^5-m^4  is divisible by n
SUFFICIENT

2)  m^4-2m^3+m^2=n^2+11 
 m^4-2m^3+m^2 = m^2(m^2-2m+1) = m^2(m-1)^2 =n^2+11 
 m^6-m^5-m^4 = m^4(m^2-m-1) = m^4{(m-1)^2+m}  
NOT SUFFICIENT

IMO A

GMATGuruNY · Answer

Is  (m^4)(m^2-m-1)  divisible by n?

Statement 2:
 m^4-2m^3+m^2=n^2+11 
 m^2(m^2-2m+1)=n^2+11 
 m^2(m-1)^2=n^2+11 
 m^2(m-1)^2-n^2=11

Since m and n are integers,  m^2(m-1)^2  and  n^2  are two perfect squares with a difference of 11.
Make a list of perfect squares:
1, 4, 9, 16, 25, 36, 49...
Only 36 and 25 have a difference of 11.
Thus:
 m^2(m-1)^2=36 
 n^2=25  --> n=±5

m^2(m-1)^2=36 
 m(m-1)=±6

Case 1:  m(m-1)=6 
 m^2-m=6 
 m^2-m-6=0 
 (m-3)(m+2)=0 
 m=3  or  m=-2

Case 2:  m(m-1)=-6 
 m^2-m=-6 
 m^2-m+6=0 
No integer solutions.

If m=3, then  (m^4)(m^2-m-1)=81*5 
If m=-2, then  (m^4)(m^2-m-1)=16*5 
In each case, the resulting product is divisible by n=±5.
Thus, the answer to the question stem is YES.
SUFFICIENT.

bumpbot · Answer

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If m and n are non-zero integers, is m6-m5-m4 divisible by n? 1) m2

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