find the angle between vectors U= <2,3> and V= <1, -5>

Answer 1

cos T = U dot V / ( |U|* |V| )
= (2-15) / (sqrt 13 + sqrt 26)
= -13 / (sqrt 13 + sqrt 2 sqrt 13)

= -13/ [sqrt 13 (1 + sqrt 2) ]

Answer 2

would that be 88 degrees, 45 degrees, 135 degrees, or 92 degrees?