Answer
The result agrees with the fact that $\cos{0} = 1$
Work Step by Step
Addition formula
$$\cos{(A+B)}= \cos{A} \cos{B}-\sin{A}\sin{B}$$
$\cos{(A-A)}= \cos{A} \cos{(-A)} - \sin{A} \sin{(-A)}$
$\cos{(A-A)}= \cos{A} \cos{A} - \sin{A} (-\sin{A})$
$\cos{(A-A)}= \cos^2{A}+ \sin^2{A} = 1$
The result agrees with the fact that $\cos{0} = 1$
