Question

In ∆ABC,AB=3cm,BC=2cm,AC=4cm.Calculati cos(A).
Teorema cosinusului:BC la2=AB la 2+AC la 2-2AB*AC*cos( Va rog ajutati-ma

Answer 1

$BC^{2}=AB^2+AC^2-2*AB*AC*cosA \\ 4=9+16-2*3*4*cosA \\ 4-9-16=-24*cosA \\ -21=-24*cosA \\ cosA= \frac{21}{24} \\ cosA= \frac{7}{8}$