Given Resultant of Two Forces

Question

Two forces of 17 N and 11 N have a resultant force of 25 N. What's the angle between the two forces?

Answer 1

25^2= 17^2 +11^2 -2(17)(11)cosD

solve for D

625 = 289+121- 374cosD

215= -374cosD

cosD=- 215/374

D= arccos(-215/374)= about 125.090 degrees

angle between them - 180-125.090= 54.910 degrees

Answer 2

You can use the Law of Cosines to determine this:

25² = 17² + 11² - 2(17)(11)cos(θ)

625 = 289 + 121 - 374cos(θ)

215 = -374cos(θ)

cos(θ) = -(215/374)

θ = cos^-1(-(215/374)) = 125°