maple help..pls (1 Viewer)

[lilkatie]

hello all
I have been trying for several hours to do two qs on maple:
how do i
a) find the nth derivative of a function at x=0???
I can find the nth derivative, but can't get it to evaluate at x=0 and give me a number!!
b) A function is defined as f(x) = (6sinx + cosx)e^(-3ax) where a is a +ive real no.
use the assume command to find teh exact integral of f(x) from 0 to infinity. Call this integral ANSB.
What is the exact value of the limit of a times ANSB as a tends to infinty?

please can someone tell me how i do these, im so stuck and can't find how to do it anywhere
thanks

 

[sikeveo]

Find the derivate of the function by b:= diff(f, x$n); where f is the function, and n is the nth derivative. Then type eval(b, x=0);

What you have done differentiated and got the nth derivative by the first statement, then in the 2nd statement you have evaluated x=0 w.r.t to the function b, which you assigned in the first statement.

No idea about the last one sorry.

 

[lilkatie]

cheers thanks for that =)
can anyone do the 2nd one?

 

[gman03]

assume (a > 0);
assume (b > 0);

f := x -> (6sinx + cosx)e^(-3ax);

ANSB := limit ( Int(f(x), x=0..b) , b=infinity);

? don't quote me on this, havn't use maple since 1st year

 

[elfm]

assume (a > 0);
assume (b > 0);

f := x -> (6sinx + cosx)e^(-3ax);

ANSB := limit ( Int(f(x), x=0..b) , b=infinity);

? don't quote me on this, havn't use maple since 1st year

for the assume thing you gotta put in 'real' with a comma before or after (i forget but i think it's after) a>0 as well.

i forgot how to do the main bit but it's probably right

and you gotta put it in exact terms as well which can be simplying found by looking at the book

 

[lilkatie]

thanks
but i still can't work out the 2nd one =( err i hate maple

 

[redslert]

Ask §eraphim, his the maths computering guy around here....

http://community.boredofstudies.org/members/%E2%A7eraphim/

 

[menty]

use EXP. e wont get u anywhere

 

[jemsta]

yeah i also need a bit of help with this question
a function is defined by A function f is defined by:
-81*x^6+145*x^5+213*x^4+311*x^3-252*x^2+55*x+267/
-44*x^7+35*x^6+583*x^5-967*x^4+242*x^3-210*x^2+513*x+1188
at which value of x does f(x) have an essential discontinuity?
how would i do that in maple?

 

[jemsta]

what happened to your z?

 

[sikeveo]

If we want to find the smallest value for which one equation equals another...?

We graph it, but then how can we find where the lines intersect? I can't be very accurate via inspection...

 

[jemsta]

say for example, if the two lines intersect between 2 and 3, then you keep decreasing the value till u get the answer to 3 decimal places
eg, ({p1, p2} x=2..3})
then ({p1, p2}, x=2..2.5})
just keep decreasing its value till u get the correct answer

 

[sikeveo]

That's just decreasing the range for the graph, you can't really judge it visually. There must be an easier way by calculating. (which is what im after)

 

[gman03]

Subtract both equations to obtain a third equation, then find the smallest root of it.

i.e. y1 = f1(x), y2 = f2(x), find root of y3 = y1 - y2

 

[sikeveo]

Surely maple must have the function i mentioned.