Step-by-step explanation:
In circle with centre O.
[tex]OA \cong OB.. (Radii\: of \:same \:circle) \\
\therefore m\angle OAB = m\angle OBA =28°\\
(m \angle 's \:opposite \:to \:congruent \:sides \:\\are \:equal) [/tex]
[tex] m \angle AOB = 180°-(m\angle OAB + m\angle OBA)\\
\therefore\: m \angle AOB = 180°-(28° + 28°)\\
\therefore\: m \angle AOB = 180°-56°\\
\therefore\: m \angle AOB = 124°\\
m \angle ACB = \frac{1}{2} \times m \angle AOB[/tex]
[tex](m\angle\: formed\: on\: the \:circle \:\\is\: half\: the\:\angle\: formed\: at\: the \:center\: \\of \:the \:circle)[/tex]
[tex] \therefore\: m \angle ACB = \frac{1}{2} \times 124°\\
\therefore\: m \angle ACB = 62°\\[/tex]
