math problem percale

Question

Label the pair of vectors as orthogonal, parallel, or neither:  v = 7i + 3j, w = -18i + 2j

Answer 1

v= 7i +3j, w = -18i +2j

angle = about 106.86 degrees which is neither orthogonal or parallel

angle = tan^-1(3/7) + 90- tan^-1(-2/18) = about 90-23.2 + 83.66=66.8+83.66

= 151.46

the more traditional method:

cosT = vw/|v||w| =dot product divided by product of magnitudes

= (3x2 -18x7)/|v||w| = (6-126)/sqr58sqr328) = -120)/sqr58x373= -120/147.09= -0.815

T= cos^-1(-.815) =180-35.33

= 144.67 degrees

145 or 151?

both look visually about right from a graph of the vectors

they're also somewhat "close" but there' an arithmetic error

or two somewhere