Question

Calculati cos A al ∆ABC. AB=4;BC=7;AC=5.

Answer 1

Avem teorema cosinusului:

$BC^2=AB^2+AC^2-2*AB*AC*cosA$

Inlocuim ce avem
$49=16+25-40*cosA \\ 49=41-40*cosA \\ 8=-40*cosA \\ cosA= \frac{-8}{40}=- \frac{1}{5}$