finding value of fraction

defeated_soldier

Junior Member
Joined
Apr 15, 2006
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130
f(x)=9^x/(9^x+3) . Find the value of

f(2/57)+f(3/57)+f(4/57)+....+f(54/57)+f(55/57)

1)1
2)55/(57)^54
3)27
4)None of these


i dont see any clue to solve it .

I need

(1) how to attack this problem ?

(2)
can i use some brute force or rough method to choose the right answer from above without solving the problem completely ?
 
Hey, long time no see, Mathsoldier !

The numerators are from 2 to 55.
Formula for sum of consecutive whole numbers from 1 to n is n(n+1)/2.

The numerators then add up to: 55*56/2 - 1 = 1539;
1539 / 57 = 27

Remember that a/x + b/x = (a+b)/x
 
Denis said:
Hey, long time no see, Mathsoldier !

The numerators are from 2 to 55.
Formula for sum of consecutive whole numbers from 1 to n is n(n+1)/2.

The numerators then add up to: 55*56/2 - 1 = 1539;
1539 / 57 = 27

Remember that a/x + b/x = (a+b)/x

Hi,
...but there was a function and the functional behaviour is given ....you ignored that in this summation .


Your solution is perfect if there were no function involved .

did you overlooked that ?

please explain.
 
defeated_soldier said:
f(x)=9^x/(9^x+3)
Does the above mean either of the following?

. . . . .f(x) = 9<sup>x</sup> / (9<sup>x</sup> + 3)

. . . . .f(x) = 9<sup>x</sup> / 9<sup>x + 3</sup>

Thank you.

Eliz.
 
stapel said:
defeated_soldier said:
f(x)=9^x/(9^x+3)
Does the above mean either of the following?

. . . . .f(x) = 9<sup>x</sup> / (9<sup>x</sup> + 3)

. . . . .f(x) = 9<sup>x</sup> / 9<sup>x + 3</sup>

Thank you.

Eliz.


yea, . . . . .f(x) = 9<sup>x</sup> / (9<sup>x</sup> + 3)
 
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