perhatikan gambar lingkaran dengan pusat O. jika besar

[tex]\ \textless \ BOD= 180^{o}[/tex]
maka
[tex]\ \textless \ AOB=180^{o}-\ \textless \ AOD\\ \ \textless \ AOB=180^{o}-56^{o}\\ \ \textless \ AOB=124^{o}\\[/tex]
sehingga,
[tex]\ \textless \ ACB= \frac{1}{2} \times \ \textless \ AOB \\ \ \textless \ ACB= \frac{1}{2} \times 124^{o} \\ \ \textless \ ACB=62^{o}\\[/tex]