Sine they are at right angles to each other, therefore “theta”= 90°. Using our cosine rule to look for our resultant force.
Explanation:
A^2=B^2+C^2 - 2BC COSthetha
A=resultant force; B=3N; C=4N; COS90=0.
A^2=3^2+4^2 - 2×3×4×0
A^2=9+16–0
A^2=25
A=√25
A=5N.