Step-by-step explanation:
[tex] {13}^{2} = {10}^{2} + {11}^{2} - 2 \times (11)(10) \cos(a) \\ 169 = 100 + 121 - 110 \cos(a) \\ 52 = 110 \cos(b) \\ \cos(b) = \frac{26}{55} \\ b = 61.78 \: degrees[/tex]
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