Substitution after differentiation (easy)?

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Mark
Mark 2012-6-4
I am trying to substitute the variable x after differentiating y with respect to x. Any ideas on the final step?
>> syms x;
>> y=5*x^2+6*x-3;
>> y1=diff(y,x);
after this I cannot use
>> x=3;
>> y1
because this just gives me y1 in terms of x

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采纳的回答

Walter Roberson
Walter Roberson 2012-6-4
subs(y1)
Caution: the result in this case would be a symbolic number; use double() on the result if you need a floating point number that MATLAB itself can compute with.

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