Homework Help: Math: Derivatives

Posted by Nick on Sunday, April 8, 2012 at 2:56pm.

Use the shortcut rules to mentally calculate the derivative of the given function
f(x) = −x + (3/x) + 1

After deriving it, I got
-1+(0/1)+0= -1
But this answer is wrong, and I don't know why.
Thank You

Math: Derivatives - MathMate, Sunday, April 8, 2012 at 3:51pm
The derivative of f(x) is
-1-3/x²

Don't know how you got -1, or what the question really is.
Math: Derivatives - Nick, Sunday, April 8, 2012 at 8:20pm
How did you get the answer? I don't quite understand. Thanks
Math: Derivatives - MathMate, Monday, April 9, 2012 at 4:01pm
If f(x)=g(x)+h(x), then
linearity gives
f'(x)=g'(x)+h'(x)
so
f(x)=-x + (3/x) + 1
f'(x)= (-x)' + (3/x)' + (1)'
=-1 -3/x² + 0
=-1 -3/x²
The second term is obtained by the power rule:
d(1/x)/dx = -1/x²

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