bisectionn
c <<ok>>
character*1 answer
real a,b,p,tol
print*, 'the fun
ction is',' f=x**3-x**2-4*x-3'
5 print*, 'please enter a,b,tol'
read*, a,b,tol
if (f(a).eq.0) print*, 'one of the root is ',a
if (f(b).eq.0) print*, 'one of the root is ',b
if (f(a)*f(b).gt.0.0) print*,'no root...
for Fortran