| sin( -θ ) | = | - sin θ | |
| - 1/4 | = | - sin θ | |
| 1/4 | = | sin θ | |
sin2θ + cos2θ = 1
(1/4)2 + cos2θ = 1
cos2θ = 1 - (1/4)2
cos2θ = 1 - 1/16
cos2θ = 15/16
cos θ = ±√[ 15/16 ]
cos θ = ±√15 / 4
Since sin θ is positive and tan θ is positive, cos θ must be positive.
cos θ = √15 / 4
