I just found out V = Acos(wt+phi) is made up of both radians and degrees, where w is rad/s and phi is degree. You have to convert either one to the other to calculate it. Assume phi is 0 degrees. I(t) = Icos(wt), and w is radian/s. So then capacitor impedance is -j/wC. V(t) = (I<0) * (1/wC<-90) V(t) = 1/(wC) < -90 <-- change 90 degree to pi/2 radian V(tr) = I/wC*cos(wt-pi/2) <--- this is solved using radians! Ok, then assume we change from radians to degrees. So I(t) = Icos(57.3wt). We use 57.3 since there are about 57.3 degrees per radian. Capacitor impedance then becomes -j/(57.3wC). V(t) = (I<0) * (1/(57.3wC)) < -90 V(t) = I/(57.3wC)<-90 V(td) = I/(57.3wC)*cos(57.3wt-90) <----this is solved using degrees! The resulting V(t) values do not match! Assume all values are 1. So V(tr) = 1/(1*1)cos(1-pi/2) using radians, comes out to be 0.84147. And V(td) = 1/(57.3)*cos(57.3-90) using degrees, comes out to be 0.0146. How come they don't match? They should be equivalent.