Two forces F1 and F2 are acting at right angles to . . .

Question : Two forces F₁ and F₂ are acting at right angles to each other. Then their resultant is 
a) F₁+F₂ 
b)√[F₁²+F₂²] 
c)√[F₁²-F₂²] 
d) (F₁+F₂)/2

Doubt by Avani

Solution : 

We know, the magnitude of the resultant of two force vectors is given by  
R = √[F₁²+F₂²+2F₁F₂cosθ]
Here both F1 and F2 vectors are perpendicular i.e. θ=90°
So, R = √[F₁²+F₂²+2F₁F₂cos90°]
R = √[F₁²+F₂²+2F₁F₂(0)]
R = √[F₁²+F₂²]

Hence, b) √[F₁²+F₂²] would be the correct option.