Answer in Problem Set: $2x\cdot sec^2(x)\cdot tan^2(x)$
Answer in Wolfram Alpha: $2 \cdot tan(x) \cdot sec^2(x)$
We can always solve it manually, deriving and stuff; but board exam has very limited time therefore we were told its always better to use shortcut. My Calculator, a Casio FX-991ES Plus can only evaluate Definite Derivatives but not give me the answer straightforward.
So I try:
with $x = 2.5$ radians and I get a the derivative of
Then when I use the correct answer from the problem set
and plug in $x = 2.5$, I get a different answer:
How can that be? Isn't that supposed to be the slope? How can I avoid this problem?