Expert: Paul Klarreich - 1/26/2010

Question
QUESTION: Hello! Im Reynand.

why is it that the 1st derivative of f(x)=(x^2)+x..is equal to
f(x)=4x+1...why is it that it is not equal to f(x)=2x+1...


ANSWER: I give up.  Why?

---------- FOLLOW-UP ----------

QUESTION: cuz, this is the topic that ive been studying off now...
im still, a student...i think you must review your answer if ever so that we can clearly identify or know the correct answer...
 thats all...

thanks..

ANSWER: The derivative of  f(x) = x^2 + 1  is indeed  f'(x) = 2x + 1.

Why?  The x^n rule.  

Did your teacher say it was  4x + 1?  Get a new one.



---------- FOLLOW-UP ----------

QUESTION: Actually i used the y=nx^(n-1).....

I'm only having a research for that cause our teacher gave us an advanced topic, including this topic....

for example y=[3/(x)^(1/2)]+[3x^10]+80
it is equal to y'=[-3/2(x^3/2)]+30x^9


Answer
QUESTION: Actually i used the y=nx^(n-1).....

Yes, that is the x^n rule.  But it says that if  y = x^n,
then y-PRIME = ....

I'm only having a research for that cause our teacher gave us an advanced topic, including this topic....

for example y=[3/(x)^(1/2)]+[3x^10]+80
it is equal to y'=[-3/2(x^3/2)]+30x^9

>> Yes, that is OK.