How to substitute x by an integer in a derivative function

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Rodrigo Toledo
Rodrigo Toledo 2021-3-29
评论： Paul 2021-3-30
I have a function:
syms x
f(x) = (tan(x^2 + 3*x))^2
a = diff(f(x))
Now i want to calculate the a when x=1. How can i do it?
i tried a(2) but didnt work.
Thanks

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采纳的回答

Andreas Apostolatos
Hello,
To evaluate symbolic expression 'a' at 'x = 1' you can use function 'subs', namely,
a_at_1 = subs(a, 1);
I am not sure why you tried typing 'a(2)' since you are trying to evaluate 'a' at 1.
More information about function 'subs' you can find in the following documentation page,
https://www.mathworks.com/help/symbolic/subs.html
I hope that this helps.
Kind Regards,
Andreas
  2 个评论
Paul
Paul 2021-3-30
You can also define a to be a function of x and then evaluate it at the value of interest
>> syms x
f(x) = (tan(x^2 + 3*x))^2
a(x) = diff(f(x))
f(x) =
tan(x^2 + 3*x)^2
a(x) =
2*tan(x^2 + 3*x)*(2*x + 3)*(tan(x^2 + 3*x)^2 + 1)
>> a(1)
ans =
10*tan(4)*(tan(4)^2 + 1)

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