I read that if the direction of velocity is perpendicular to the acceleration the magnitude doesnt change and if they are parallel the direction doesnt change and if they are neither both change
if we have v1=6i+8j ,|v1|=10 theta with positive x =53
v2 =10j ,|v2|=10 theta with positive=90
delta v = -6i+2j theta with positive=161.5
since the direction of the acceleration is the same direction of the change of velocity
and the magnitude of the velocity didnt change shouldnt delta v be perpendicular to v1
but the angle is 108.5 why is that?