Question

Trigonometria.
Determine o cosseno do ângulo BÂC.

Answer 1

Iae!

lei dos cossenos.

${a}^{2} = {b}^{2} + {c}^{2} - 2 \times b \times c \times cos \: \alpha \\ \\ {8}^{2} = {3}^{2} + {6}^{2} - 2 \times 3 \times 6 \times cos \: \alpha \\ \\ 64 = 9 + 36 - 36cos \: \alpha \\ \\ 64 = 45 - 36cos \: \alpha \\ \\ 64 - 45 = - 366cos \: \alpha \\ \\ 19 = - 36cos \: \alpha \: \: \: \: \times ( - 1) \\ \\ 36cos \: \alpha = - 19 \\ \\ cos \: \alpha = - \frac{19}{36}$

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