Friday, June 15, 2012

Find f(x) if f'(x) = 3x^2 - 5x + 1 if f(0) = 4

Since the first derivative is a quadratic, then the original
function is a polynomial of 3rd order.


We'll put
f(x):


f(x) = ax^3 + bx^2 + cx + d


To
determine f(x), we'll have to calculate the coefficients a,b,c,d.


We
know, from enunciation, that f(0) = 4.


f(0) = d =>
d = 4


Now, we'll differentiate
f(x):


f'(x) = 3ax^2 + 2bx + c


From
enunciation, we know that: f'(x) = 3x^2 - 5x + 1   


We'll
put:


3ax^2 + 2bx + c = 3x^2 - 5x +
1   


We'll put the correspondent coefficients as
equal:


3a = 3


a =
1


2b =
-5


b =
-5/2


c =
1


The original function
is:


f(x) = x^3 - 5x^2/2 + x +
4

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