Question

Please solve the given question

I know the answer but I need explanation also

PLEASE help ​

Answer 1

R² = F1² + F2² + 2 F1.F2 cos α ⇒cosinus

F1 and F2 perpendicular, α = 90°, cos 90° = 0

`\tt R=√(3^3+4^2)=5`