Final answer:
The quadrant is either the third or fourth quadrant and sin θ = -3/5.
Step-by-step explanation:
Given that cos θ = 4/5 and sin θ is less than 0, we can determine the quadrant of the terminal side of θ using the signs of the sine and cosine functions in each quadrant. Since sin θ is negative, it means that θ lies in either the third or fourth quadrant.
To find sin θ, we can use the Pythagorean identity: sin^2 θ + cos^2 θ = 1.
Substituting cos θ = 4/5 into the equation, we can solve for sin θ:
sin^2 θ + (4/5)^2 = 1
sin^2 θ + 16/25 = 1
sin^2 θ = 1 - 16/25
sin^2 θ = 9/25
sin θ = ± 3/5
Since sin θ is negative, we can conclude that sin θ = -3/5.