∠ AFE=90 °
[m]cos ∠ FAE=\frac{AF}{AE}=\frac{3}{5}[/m]
[m](\vec{AE}+\vec{FC})\cdot \vec{AC}=\vec{AE}\cdot \vec{AC}+\vec{FC}\cdot \vec{AC}=[/m]
[m]=|\vec{AE}|\cdot|\vec{AC}|\cdot cos∠ FAE +|\vec{FC}|\cdot |\vec{AC}|\cdot cos0 ° =5\cdot 8\cdot \frac{3}{5}+5\cdot 8\cdot 1=[/m]
[m]=24+40=64[/m]
О т в е т. Е)