What am I doing wrong ?
Shouldn't the last two values be equal ?
Besides, r^65 gives different values depending on decimal places configured in option menu
r^65=64.992 (3 decimal places)
r^65=64.9994 (4 deccimal places)
third decimal isn't the same!!

Open in SMath Cloud

Hello,

Will is right. The results of solve() function depend on the number of displayed decimals. In general, SMath does not have the option for setting the calculating precision with the applied numerical functions. I think that Will is using 0.89 version. Here is the same example with 0.89.8 version
r←solve(65-x^5,x)
r=2.304
r^5=64.917
and
r=2.30453161980214
r^5=64.9999999999999
It seems that something has been changed in between. My advice is to use the four argument solve() function, whenever posible. Here it is:
r←solve(65-x^5,x,2,3)
r=2.305
r^5=65
Pay attention that solve() will sometimes fail in spite of quite good searching range given. Some playing with the range (third and fourth argument) might be needed.
Regarding the nonlinear equations, one can use roots() as well. Here is the same example solved with roots():
r←roots(65-x^5,x)
Three decimal places:
r=2.305
r^5=65
Fifteen decimal places:
r=2.30453161980214
r^5=64.9999999999999
Sometimes a three argument roots() version might be more appropriate (if the two argument roots() fails)
r←roots(65-x^5,x,2)
r=2.305
r^5=65

Regards,
Radovan

Edited by user 26 April 2011 10:45:11(UTC)  | Reason: Not specified