ANSWER:
To find the size of the angle when you know the cos, use cos-1(0.324).
On hand-held calculators use (2nd) (cos) , enter 0.324 to get the answer: 71.1°.
On this calculator, use (2nd) (acos) and then enter the value.
“acos” means “arc cos”, which is the inverse cosine.
Similarly, find sin-1(0.123) and tan-1(0.783), using (2nd) (asin) and (2nd) (atan).