program newtc
c
c -- square and cube root of 2 by newton-s method
c
      logical error
      integer out
      real x
      external sqr2, cube
      common /inout/ out
c
      out = 6
      write(out,*) ' newton-s method'
      x = 2
      call newton(x, sqr2, error)
      write(out, 102) x
      call newton(x, cube, error)
      write(out, 105) x
99    stop
102   format(/' the square root of 2 is ', f8.5)
105   format(//' the cube root of 2 is ', f8.5)
      end
      subroutine cube(x, fx, dfx)
c
c -- the cube root of 2
c
      real x, fx, dfx, x2
c
      x2 = x * x
      fx = x2 * x - 2
      dfx = 3 * x2
      return
      end