For this problem you will probably want to use the inverse cosine
function (acos) and the square root function (sqrt) which are defined
in "math.h".  You need to put "#include <math.h>" in the beginning of
your program to use these functions.  

You will also need to use the "-lm" parameter when compiling with gcc.
This tells gcc to link your program to the math library.

For example: 
> gcc -o prog prog.c -lm


a) Implement a function called dot that computes the dot product of
two vector:

double dot(int n, double A[], double B[])

Here n is the size of the arrays A and B which represent the
two vectors.

b) Use the dot product function from above to write a function that
computes the angle between two vectors:

double angle(int n, double A[], double B[])

You can use the formula A*B = |A||B|cos(theta).  Where A*B is the dot
product of A and B, |A| and |B| are the norms of A and B and theta
is the angle between the vectors.

c) Write a program that computes and prints the angle between:
(0,0,0,0,1) and (0,1,0,0,0),
(0,0,0,0,1) and (0,0,0,0,2),
(1,5,2,0,0) and (2,7,2,0,0).