I'm currently taking a calculus course and I'm supposed to be able to graph a derivative of a function using a graphing calculator. The textbook says to input nDer(f(x),x) but I can't seem to figure it out. I've tried various things and sometimes it comes out as a line at y=0 but most of the things I've tried don't graph anything at all. Can someone explain to me how to graph a derivative of a function, such as f(x)= lnx?

(09-28-2014 07:35 PM)mayradio0508 Wrote: [ -> ]I'm currently taking a calculus course and I'm supposed to be able to graph a derivative of a function using a graphing calculator. The textbook says to input nDer(f(x),x) but I can't seem to figure it out. I've tried various things and sometimes it comes out as a line at y=0 but most of the things I've tried don't graph anything at all. Can someone explain to me how to graph a derivative of a function, such as f(x)= lnx?

Two ways, you'll need the derivative template [Template Key, 1st row, 4th column]

Let d represent the "curvy derivative symbol".

Textbook entry:

F1(X) = LN(X)

F2(X) = (d F1(X))/(dX=X)

or directly:

F1(X) = (d LN(x))/(dX = X)

Algebraic Entry:

F1(X) = d( LN(X), X=X)

This seems like the most logical way to ask the calc to plot a function and its derivative... the syntax seems completely logical and "correct", but it just doesn't work.

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But yeah; putting dX=X in the denominator works:

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Of course this works as expected in the CAS environment... but that's old news here.

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