How can I plot $A(a,b) = 2\cos(2b-a+1)$

Question

$A_{1}(a,b) = 2\cos(2b-a+1)$

$A_{2}(a,b) = 2\cos(-2b-a+1)$

$A_{3}(a,b) = 2\cos(2b+a+1)$

I want to know which waves are moving $+a$ or $-a$

Thanks