\TWOVECTORSANGLE(1,1)(0,1){\sol}
$\sol$ radians
\RADtoDEG{\sol}{\degsol}
(or $\degsol$ degrees)

\TWOVECTORSANGLE(1,0,0)(0,1,0){\sol}
$\sol$
\RADtoDEG{\sol}{\degsol}
(or $\degsol$ degrees)