
The reference angle for an angle in quadrant 4 is equal to 360 degrees minus the angle.
In this case, the angle is 315 degrees and the reference angle is 360  315 = 45 degrees.
The trigonometric functions of 315 degrees are the same as the trigonometric functions of 45 degrees except for the signs.
Sin(315) = Sin(45) = .707106781
Cos(315) = Cos(45) = .707106781
Tan(315) = Tan(45) = 1
The sine function is negative because the opposite side is below the xaxis.
The cosine function is positive because the adjacent side is to the right of the yaxis.
The tangent function is negative because it is equal to the opposite side divided by the adjacent side and a negative divided by a positive is negative.
