Explicație pas cu pas:
teorema cosinusului:
[tex]{c}^{2} = {a}^{2} + b^{2} - 2ab \cos(C) [/tex]
[tex]=>\cos(C) = \frac{{a}^{2} + b^{2} - {c}^{2}}{2ab} [/tex]
=>
[tex]\cos(C) = \frac{ {AC}^{2} + {BC}^{2} - {AB}^{2}}{2AC \times BC} = \frac{ {8}^{2} + {18}^{2} - {12}^{2}}{2 \times 8 \times 18} = \frac{61}{72} [/tex]
