solving variable in exponential equation

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SP
SP 2019-2-4
评论： Stephan 2019-2-4
i am trying to use the equation: y = ae^rt; to solve for t; y = final population, a = initial population, r = rate increasing. i'm using editor but it is not working. i know the answer to my equation is around 210, however my code below is not working:
sysm y a r t
y == a * ((exp((r*t));
a = 300;
r = .10;
y = 600;
solve t
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Walter Roberson
Walter Roberson 2019-2-4
The paper uses values around 300 that are no-where to be found in the 600-ish values you posted.
SP
SP 2019-2-4
i apoligize a = 300, that was my mistake

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回答（2 个）

KSSV
KSSV 2019-2-4
syms y a r t
eqn = y == a * ((exp((r*t))));
S = solve(eqn,t) ;
a = 600;
r = .10;
y = 600;
S = subs(S,a) ;
S = subs(S,r) ;
S = subs(S,y) ;
Stephan
Stephan 2019-2-4
编辑：Stephan 2019-2-4
syms t
a = 600;
r = .10;
y = 600;
eq = y - a * (exp(r*t)) == 0;
tsol = solve(eq,t)
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Stephan
Stephan 2019-2-4
error is corrected. the solution is zero. this is obviously.

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