cos(A) = 0.97125
apply "acos" the arc-cosine, same as cos^-1, on both sides:
acos(cos(A)) = acos(0.97125)
A =acos( 0.97125 )
$$\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{cos}}^{\!\!\mathtt{-1}}{\left({\mathtt{0.971\: \!25}}\right)} = {\mathtt{13.772\: \!176\: \!508\: \!038^{\circ}}}$$
.
