## 927 Reputation

4 years, 143 days

## Try...

evalf(eval(-Gradient(uval(r, t), 'cylindrical'[r, theta, z]), [r = 2, t = 4]));

## Workaround.....

I don't know why there is a problem here,but you use workaround:

eval(solve({-1 < b, a < -1, b < 0, -z < a}), z = infinity);

#{-1 < b, a < -1, b < 0, -a < infinity}

## It works for me (see the attached file)....

It works for me (see the attached file).

plot2019.1.mw

WHY2019.1.mw

Maybe this helps

## Just lucky.....

I honestly don't know why it worked.

First I tried Maple help: ?dsolve,system and I use option: useInt , but it dosen't work(bug or what?).If I use useint it worked.That's all.

## ...?...

Maybe this helps.

## Workaround:...

restart;

Digits := 20;

sol := solve(simplify(expand(convert(sin(9*x - 1/3*Pi) = sin(5*x - 1/6*Pi), exp))), [x], explicit, allsolutions);

seq([x = simplify(allvalues(identify(evalf(simplify(Re(rhs(sol[j][1])))), all)))], j = 1 .. nops(sol));

#[x = Pi*_Z7 + 1/4*Pi], [x = Pi*_Z6 + 1/24*Pi], [x = Pi*_Z6 - 11/24*Pi], [x = Pi*_Z5 - 1/28*Pi], [x = Pi*_Z5 + 3/28*Pi], [x = #Pi*_Z5 + 11/28*Pi], [x = Pi*_Z5 - 13/28*Pi], [x = Pi*_Z5 - 9/28*Pi], [x = Pi*_Z5 - 5/28*Pi]

## @Carl Love  I copy and paste code ...

I copy and paste code to Maple and dosen't work?

## @Carl Love  It make sense to ...

It make sense to me.I don't  mean a discrete derivative.

## @vv  Yes I want differentiate with...

Yes I want differentiate with respect to a natural number.

## Maybe.....

@Rouben Rostamian

See attached file.

## Yes, I also want  find many th...

Yes, I also want  find many things?

Please post a clear example of input and desired output. Nobody likes to guess...

## Please paste copy&pastable code inst...

Please paste copy&pastable code instead of screenshots. It is not fair to the people who are trying to assist to make them need to retype all your content based on some images.

You can upload a worksheet by using the green up-arrow on the toolbar of the MaplePrimes editor.

## @golnaz You say: ((sqrt(a*e^(-...

You say:

((sqrt(a*e^(-2*x)+a))-sqrt(a)));

# Error, unable to match delimiters ???

You wrote in the question: (sqrt(exp(-2*x) + a) - sqrt(a)) then you wrote:  ((sqrt(a*e^(-2*x)+a))-sqrt(a))),it's not same expression ?

## In Mathematica it's ease to do: &...

In Mathematica it's ease to do: