Answer to Question #51716 in Vector Calculus for tiff

Question

a=2i-3j-k, b=i+4j+3k then what;s their angle? if i use dot product formula it comes arc cos[(-sqrt(13)/{(2*sqrt(7)}]

and if i use cross product formula then arc sin[(sqrt(15/28)] . two angles are not same if i convert to degree , then 1st one comes 132.951978120924 and the 2nd one 47.048021879076. it become equal that time if (180-47.048021879076) . because sin(180-x)=sin x . but for inverse function , we use the least value. like arc sin(1/2)= 30 degree, not 150 degree. so if i think at this angle the angle can't be equal. so which one is correct?