Ive tried to enter the calculation in a calculator

asin(35.4)(sin(51)/31.2)

why do i get an error??

Since the trigonometric functions are based on a unit circle,

it can't tell you what the arcsin of 35.4 is.

You can only take the arcsin of a value between -1 and 1 (including -1 and 1).

I would not say that trigonometric functions are based on the unit circle but it is certainly true that

asin(x) only is defined (has a value) for

\(-1\le x\le1\)