Consider the sequence of functions f_n (x)= x / (1+nx^2) let f = lim f_n. Compute f'_n and find all values of x such that f'(x)=lim f'_n (x)
Follow Math Help Forum on Facebook and Google+
Can you state 'f' explicitly? Is it constant, linear, what? Can you find f'_n, generally?
f_'n (x)=(1-nx^2)/(1+nx^2 )^2 and f=0
Last edited by veronicak5678; November 16th 2011 at 06:58 PM.
Very good. You're almost there. Where is the derivative zero?
The derivative is zero when nx^2 =1, or when x=(1/n)^1/2 But isn't lim f' =0 for all x?
Let's try to remember which variable is moving. Are we talking about x approaching zero or n increasing without bound? AT x = 0, what is the limit of f'_n as n increases without bound?
At x=0, f'_n =1
Right, and that's not zero (0), is it? I believe you were done with this problem when you said this: "x=(1/n)^(1/2)"
I guess I thought there was more to it. Thanks for your help.
View Tag Cloud