In the figure below, O is the center of the circle. Find the value of ACB.

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Step 1: Use the cosine rule to find $\angle Q$.

$$\cos Q = \frac{PQ^{2} + QR^{2} - PR^{2}}{2 \cdot PQ \cdot QR}$$

Step 2: Substitute the side lengths $PQ = 8.3$ cm, $QR = 9.2$ cm, $PR = 7.6$ cm.

$$PQ^{2} = 8.3^{2} = 68.89\, \mathrm{cm}^{2}$$ $$$$