Hi everyone, I've discovered quite a strange function in my textbook. I compared the calculator's calculated derivatives (Math->nDriv) with my calculus derivative and found that the two are almost 2000 units off! Up until now I've been trying to figure out the problem, but to no avail, I cannot find the solution. Here's the function:(adsbygoogle = window.adsbygoogle || []).push({});

f(x)=Cos2(tanx)

using derivative shortcuts, I came up with

f'(x)=-2cos(tanx)sin(tanx)sec2x

as my derivative function

plugging in 11, I came up with -23921.7403... as the derivative at 11

however, when i compare this with the calculator's nDriv answer, it is drastically different:

nDriv(f(x), x, 11)= -342.6

that's difference in the 2000 units... i mean, i compared the rest of the values at various other points and the most off they have been is around .001; only at 11 does this great gap occur.

Does anyone have any idea what the problem is? Any tips and help will be appreciated. If you have a ti-89 or another version of the calculator, please feel free to try it on your calculator and post if you have the same result as me.

Thanks so much,

Alex

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# Homework Help: TI-84 error? Or my own fault?

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