why this is Index exceeds matrix dimensions?

Vc = 2
Vm = 1.5
fc = 100
fm = 10
ts= 1/1000
n = 0:99
t = ts*n


vc = Vc*cos(2*pi*fc*t);
vm = Vm*cos(2*pi*fm*t);
vam = Vc*cos(2*pi*fc*t)+(Vm/2)*cos(2*pi(fc-fm)*t)-(Vm/2)*cos (2*pi(fc+fm)*t);

Answer 1

[KALYAN ACHARJYA]

Vc = 2;
Vm = 1.5;
fc = 100;
fm = 10;
ts= 1/1000;
n = 0:99;
t = ts*n;
vc = Vc*cos(2*pi*fc*t);
vm = Vm*cos(2*pi*fm*t);
vam = Vc*cos(2*pi*fc*t)+(Vm/2)*cos(2*pi*(fc-fm)*t)-(Vm/2)*cos (2*pi*(fc+fm)*t)
%......................................^...........................^

Answer 2

[KSSV]

Note this step:

cos(2*pi(fc-fm)*t)

There * is missing pi and (fc-fp)

Change that one to

cos(2*pi*(fc-fm)*t)

Vc = 2 ;
Vm = 1.5 ;
fc = 100 ;
fm = 10 ;
ts= 1/1000 ;
n = 0:99 ;
t = ts*n ; 
vc = Vc*cos(2*pi*fc*t);
vm = Vm*cos(2*pi*fm*t);
vam = Vc.*cos(2*pi*fc*t)+(Vm/2).*cos(2*pi*(fc-fm)*t)-(Vm/2).*cos (2*pi*(fc+fm)*t);

[madhan ravi]

Note: * is enough for scalar multiplication.