if anyone knows how to input this equation in the ti 89 so i can ∠get the answer because everytime i put it in i get a "dimension error"

this is the way i put it into the ti 89 [6.247,∠51.34] * [0.78086, ∠-51.34]/(2)

and i get a dimension error

 

If i remember properly, you have to put parenthesis around the angle argument when using the '∠' character.

i.e.

89 [6.247,∠(51.34)] * [0.78086, ∠(-51.34)]/(2)