thx josh. so can i just say "root can't be solved"? the max iterations for secant method is 4times to get the 1st postive root. can i just change the number of iterations ?

Since the signs of the function values of both Xi and Xi-1 are equal you can't

use those two values as initial approximations for the root value; at least you

can't use the secant method here. That's all there is to it. You either have to

find two other Xi, Xi-1 values or you have to use another approximation method.

kind regards,

Jos