n = 1 ∑ 2 0 1 5 [ ( − 1 ) n ( n ! n 2 + n + 1 ) ]
If the summation equals to − a − c ! b for positive integers a , b , c
What is the minimum value of a + b + c ?
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Math man toogle the latex and copy the latex and edit your question because the 1 you have written looks like 2
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OK , it is 4032:)
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thanks for the help , please do it quickly so others don't confuse and from toogling other's people latex you can learn to write in latex
My break is more numerical for numerical analysis. Not as good as f (n) + f (n + 1).
Did exact same!!! Gd solution...
How to do it the other way
notice that if we switch 2015 to 1,3,5,7.... we see
when 2015 is 1 it is − 1 − 1 ! 2
when 2015 is 3 it is − 1 − 3 ! 4
.....
thus when 2015 is 2015 it is − 1 − 2 0 1 5 ! 2 0 1 6 )
so, a=1,b=2016,c=2015,a+b+c= 4032
So in a way you are doing mathematical induction . Good
for writing in fraction use - \dfrac{2}{1!} when encased in brackets , it will give - 1 ! 2
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toogle latex is made so that one can learn latex. thanks
/dfrac{2}{5}
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n = 1 ∑ 2 0 1 5 ( − 1 ) n ( n ! n 2 + n ! n + 1 )
n = 1 ∑ 2 0 1 5 ( − 1 ) n ( ( n − 1 ) ! n + n ! n + 1 )
− 1 − 1 ! 2 + 1 ! 2 + 2 ! 3 − 2 ! 3 − 3 ! 4 + . . . ( − 1 ) 2 0 1 5 ( 2 0 1 4 ! 2 0 1 5 + 2 0 1 5 ! 2 0 1 6 )
We can see that alternate terms cancel each other
− 1 − 2 0 1 5 ! 2 0 1 6
a + b + c = 4 0 3 2