SOLUTION: Find f(x) given that f'(x) = x^3 − 2√x, f(1) = 4

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Question 1099289: Find f(x) given that
f'(x) = x^3 − 2√x, f(1) = 4

Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
The derivative of a sum of functions is the sum of the derivatives,
so the same applies to antiderivatives,
So to find a function with x%5E3-2sqrt%28x%29 for a derivative,
we need to find what function has for derivative x%5E3 ,
and what function has for derivative sqrt%28x%29=x%5E%221+%2F+2%22 .
We also know that if we find a function with x%5E3-2sqrt%28x%29 for a derivative,
adding any constant C , we get another function with the same derivative.
We will use f%281%29=4 to figure out what constant to add.

We know about derivatives of polynomials.
For any exponent r (integer or not, as long as r%3C%3E-1 ),
if g%28x%29=x%5E%28r%2B1%29%2F%28r%2B1%29 , %22g+%27+%28+x+%29%22=x%5Er ,
and that lets us figure out the antiderivative of any x%5Er ,
except x%5E%28-1%29=1%2Fx .

So, the antiderivative of x%5E3 is x%5E4%2F4 ;
and the antiderivative of sqrt%28x%29=x%5E%221+%2F+2%22 is x%5E%223+%2F+2%22%2F%223+%2F+2%22=%282%2F3%29x%5E%223+%2F+2%22=2x%5E%223+%2F+2%22%2F3 .

So, we can see that f%28x%29=x%5E4%2F4-2%282x%5E%223+%2F+2%22%2F3%29%2BC=x%5E4%2F4-4x%5E%223+%2F+2%22%2F3%2BC
for some constant C .
Then, f%281%29=1%2F4-4%2F3%2BC .
If f%281%29=4 ,
1%2F4-4%2F3%2BC=4
C=4%2B4%2F3-1%2F4
C=61%2F12 ,
and highlight%28f%28x%29=x%5E4%2F4-4x%5E%223%2F2%22%2F3%2B61%2F12%29