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(in a past paper it asks u to solve this for -180</=theta<180, so I have solved it) Tan theta =-1, so theta = -45. Use CAST diagram to find other values of theta for -180</=theta<180: Theta (in terms of tan) = -ve, other value is in either S or C. But because of boundaries value can only be in S. So other value= 180-45=135. Do the same for sin. Sin theta=2/5 so theta=23.6 CAST diagram, other value in S because theta (in terms of sin)=+ve. So other value=180-23.6=156.4.
For tan(180 degrees), this is simply sin(180 degrees)/cos(180 degrees). To find these values, note that 180 degrees is the leftmost point on the unit circle, at y=0, x=-1, so is tan(180 degrees)=0/-1=0. Then adding 15 gives 15.
Any value for which sin(theta) = 0, i.e. theta = N*180, N being an Integer.
cos(125) = cos(180 - 55) = cos(180)*cos(55) + sin(180)*sin(55) = -cos(55) since cos(180) = -1, and sin(180) = 0 So A = 55 degrees.
It is simply the sine of the supplementary angle. If x is an angle measuring (90, 180) degrees, then sin(x) = sin(180 - x).