Displaying (small number)*(syms variable) as 0

This is an arbitrary example representing my problem

syms x;

a=0;
b=pi/2;
c=x;

R=[cos(a)*cos(b)*cos(c) sin(a)*sin(b)*sin(c)];

vpa(R)

This outputs:

ans =
 
[ 6.1e-17*cos(x), 0]

Because pi isn't exact in Matlab, then cos(pi/2) isn't exactly zero as sin(0) is, which leads to the first element in ans to be written as such, and the second element to be written exactly 0;

I've tried "digits" before vpa, "format long", changed format in preferences, but none works.

How can I edit my code such that the first element is displayed as exactly 0?

Answer 1

[Walter Roberson]

syms x;

a=0;
b=sym(pi)/2;
c=x;

R=[cos(a)*cos(b)*cos(c) sin(a)*sin(b)*sin(c)];

vpa(R)

ans = 

[Mike]

Can't believe it was that simple, thanks.

Answer 2

[Steven Lord]

Another solution, if you know one of the quantities involved is a multiple of π:

syms x;

a=0;
b=1/2;
c=x;

R=[cos(a)*cospi(b)*cos(c) sin(a)*sinpi(b)*sin(c)];

vpa(R)

ans = 

cospi computes the cosine of pi times its input without actually computing pi times its input.