Question

Cos 0 = 4/5 and sin 0 < 0. Identify the quadrant of the terminal side of 0 and
find sin 0

Answer 1

sinθ = -3/5, Quadrant IV (Option B)

Explanation:

Let's first find the sine

cosθ = adj./hyp.

Pythagorean theorem (in terms of right triangle trig) = (opp)^2 + (adj)^2 = (hyp)^2

Plug in the adjacent and hypotenuse

(opp.)^2 + 16 = 25

solve for the opposite side

opp. = 3

To find the quadrant, recall the sin <0, so the sin has to be negative.

So, your sine value is -3/5.

Sine is negative at Quadrants III and IV, so eliminate C and D.

Since your cosine value is positive, it is at Quadrant IV (Cosine is positive at the first and fourth quadrants.)

Therefore, Option B is correct.