FORTRAN 77 'Error: Unclassifiable statement at (1)'

Question

I'm a Fortran 77 learner, I'm new so don'n know much about Fortran. Our professor gave us a homework. We suppose to write a program that calculates cos(x**2). It has a Taylor expansion, so I tried to write some things but It gave me this error:

   term = term*((-1)**i)*x**2*i)/fac(2*i)                          
   1

Error: Unclassifiable statement at (1)

The hole program is:

        PROGRAM COSX_SQUARE
        IMPLICIT NONE
        INTEGER x, n, i
        REAL partial_sum, term

20      PRINT*, 'INPUT THE DEGREE'
        READ*, x
        x = x*180/3.1415

        PRINT*, 'INPUT THE CORRECTION VALUE '
        PRINT*, 'AS A NATURAL NUMBER'

        READ*, n

        i= -1
        term = 1
        partial_sum = term

10      i=i+1
        term = term*((-1)**i)*x**2*i)/fac(2*i)

        partial_sum = partial_sum + term

        IF (i .LT. n) THEN
        GO TO 10
        ELSE
        PRINT*, 'COS', x, 'SQUARE IS = ', partial_sum
        END IF

        GO TO 20

        END

Where am I mistaking? And will this program work well? Thanks in advance.

Answer 1

You are missing one bracket in your expression!

It should probably read:

term = term*(((-1)**i)*x**2*i)/fac(2*i)