We know
a
m
+
n
=
a
m
×
a
n
But there are some students who claim that
a
m
+
n
=
a
m
+
a
n
which is obviously incorrect. However, it is true for some triplets of integers,
(
a
,
m
,
n
)
. If
a
∈
[
0
,
1
0
]
and
m
,
n
∈
[
1
,
1
0
]
, then find the number of possible triplets for which
a
m
+
n
=
a
m
+
a
n
.
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excellent work
a = 0 always work for any m , n = 0 (100 ways)
For a = 0 , let a m = x , a n = y such that x , y = 0
The equation becomes x y = x + y .
Factor as ( x − 1 ) ( y − 1 ) = 1
Which gives ( x , y ) = ( 0 , 0 ) , ( 2 , 2 ) .
a m = 2 , a n = 2
Which gives ( a , m , n ) = ( 2 , 1 , 1 ) . (1 way)
Therefore, the number of ways = 1 0 1 .
same way!!
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Overrated!
if you post same way with one exclamation mark '!', then you will not be able to post your comment.... but with 2, the string size increases!! WOW! LOL!
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saaaame way!
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@Samuraiwarm Tsunayoshi – Now it's fixed by Calvin Lin that each solutions and comments must be at least 10 characters. lel
i too did it the same way!! ...hey kartik do u study at fiitjee noida??
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no, i don't! I don't go to tuition or take any coaching! Do you go there from Ghaziabad?
doesn't these "mistake gives rise to problems" help people to get tons of points in a blink .....
But if a=1, then also 100 more solutions are possible, in a similar way. So shouldn't the answer be 201?
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If a=1, then that means 1 m + n = 1 m + 1 n , implying that 1 = 2, which is definitely not true.
Same Way!!
Nice solution, yours is a little easier than mine.
Nice way of thinking.
Same Way !!
a m + n = a m + a n If a = 0 , we get 0 m + n = 0 m + 0 n From here, we can see that any value of m and n will satisfy the equation above. Therefore, all triplets in the form of ( 0 , m , n ) satisfy the equation above. There are 1 0 possible values of m and n each, so we have 1 0 0 different triplets in the form of ( 0 , m , n ).
If a = 0 , a m + n = a m + a n a m + n − a m − a n = 0 a m a n − a m + 1 − a n = 1 a m ( a n − 1 ) − 1 ( a n − 1 ) = 1 ( a m − 1 ) ( a n − 1 ) = 1 The question has stated that the triplets are integers. That means that a m and a n are both integers, which also means that ( a m − 1 ) and ( a n − 1 ) are both integers.
Now, the only possible way for two integers to have a product of 1 is to have both integers be 1, that is 1 ∗ 1 = 1
From there, we can infer that ( a m − 1 ) = ( a n − 1 ) = 1 a m = a n = 2
If a ≥ 3 , no integer value of m or n can make a m = a n = 2
If a = 1 , a m = a n = 1 for all values of m and n
Therefore, the only possible value of a that isn't 0 is 2 .
When a = 2 2 m = 2 n = 2 It is pretty obvious that m = n = 1
Therefore, the only triplet with a = 0 that satisfies the equation is ( 2 , 1 , 1 )
Finally, the total number of solutions is 1 + 1 0 0 = 1 0 1 solutions.
a m + n = a m + a n
When n = 0 and m = n ,
a m = a m − n + 1
a m − 1 = a m − n
This is invalid when m < n
When m > n there are no solutions because
If a is odd, LHS = even and RHS = odd
If a is even, LHS = odd and RHS = even
When m = n
a m − 1 = 1 ; There is a solution of ( 2 , 1 , 1 )
When a = 0
There are solutions for all m and n ; 100 triples.
Total = 1 0 1 triples
First, the case when a=0 works for all cases because 0^x=0 and 0+0=0. Also, since there are 10 possible values for m,n, there are 100 possible triples of (0,m,n).
Next for a>0, we divide both sides by a^n and get a m = a m − n + 1 . This means that the difference between a m and a m − n must be 1. However, this is only achievable if a=2 and m=n=1. The proof that this doesn't work is that there is no positive integer that when raised to a power is 1 greater than itself except for 2. Finally, we add the 100 cases when a=0 and the special case when a=2 and our total count is 101.
Side note: if an integer x>2 and integers p>n>0, x p = x p − n + 1
First we know that it will work with any combination with zero as a base so we have 1 0 × 1 0 = 1 0 0 solutions first.
Now, if we rephrase the equation:
a m + n = a m + a n
⟹ a m − 1 = a m − n
We can observe that the right side ( a m − n ) is a multiple of a and the right side is a multiple of a decreased by one. Obviously, these are not equal, except for one case:
In a = 2 , m = 1 , m = 2
2 1 − 1 = 2 1 − 1
⟹ 1 = 2 0 , Which is true.
∴ We have 1 0 0 + 1 = 1 0 1 solutions.
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Clearly if a = 0 then a m + n = a m + a n is true for all ( m , n ) Which means that a = 0 yields 1 0 ∗ 1 0 = 1 0 0 solutions.
If a = 0 we get:
a m a n = a m + a n
a m ( a n − 1 ) = a n
a n − 1 = a n − m ⇒ 1 = a n − a n − m
This implies that for some non-zero integer a , there are two integer powers of a with a difference of 1
Clearly this is only true if a n − m = 1 ⇒ a n = 2 ⇒ a = 2 ∧ n = m = 1
This then means that there are 1 0 0 + 1 = 1 0 1 possible triplets.