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# Maths Diff Question confusion Pls help watch

1. Hi All

Help needed with 2 Differentiation Questions.

Q= 2e^x + e^-2x
A= 2e^x + -2e^-2x

Why would they keep 2e^x in the answer ?
I do understand the -2e^-2x part though managed to work that one out correctly..

Q= sin(-8Q) the Q is supposed to be theta dont know how to write it on keyboard.
A= I would tend to give -8 Cos -8Q but the actual answer is

Kind regards
SZia
2. When writing down answers, it's best not to use Q=... and A=... as this is not a standard notation so it can be confusing. Instead, you can use the notation which means that if you differentiate f(x) you get g(x). So for example, you might write your answer to the first question as .

Anyway, to answer your question, when you differentiate you can use the chain rule if you're not sure. So let and so y=2u. Now . So if we differentiate we get .

For the second part, sketch a graph of y=cos(x). You'll notice that the graph is symmetrical about the y axis, so we could swap round the x and -x axes and still get the same graph. What this means mathematically is that cos(x)=cos(-x) which is a general trigonometric identity that is useful to know. So in your case, you have so using this identity we have, we can say that this is equal to . What this does is it eliminates an extra minus sign, making the answer slightly simpler.

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