Why do I get Error: File: exercise_1_b.m Line: 8 Column: 28 Unexpected MATLAB operator.

I get this error

Error: File: exercise_1_b.m Line: 8 Column: 28
Unexpected MATLAB operator.

this is my code

t = [-2.5: 0.01: -1.5];
A_c = 1;
f_c = 50;
m_t = sinc(2 * (t - 2)) - sinc(2 * (t + 2));

% b)
k_a = input('enter the value of k_a: ');
s_t = A_c * (1 + k_a * m_t). * cos(2 * pi * f_c * t);
plot(t, s_t);

If I dont use the "." operator for "s_t".

I get the

Error using  * 
Inner matrix dimensions must agree."

error.

Answer 1

[Walter Roberson]

Do not have a space between the . and the * . It is a pair of characters that must go together, .*

Answer 2

[Ahmet Cecen]

s_t = A_c * (1 + k_a * m_t) .* cos(2 * pi * f_c * t);

The operator is ".*" not ". *". That being said there are still other issues here, starting with sinc not being a function.