mathematics怎样计算极限

题目

mathematics怎样计算极限
limit[[sqrt[4 + 1/x - 1/x^2] - 1 + 1/x]/sqrt[1 + sin[x]/x^2],
x -> -infinity]；
想求极限,is incomplete; more input is needed.”怎么回事?

答案

limit[[sqrt[4 + 1/x - 1/x^2] - 1 + 1/x]/sqrt[1 + sin[x]/x^2],
x -> -infinity] ；
Syntax::sntxb: Expression cannot begin with "[sqrt[4+1/x-1/x^2]-1+1/x]/sqrt[1+sin[x]/x^2]".
Syntax::tsntxi: "[sqrt[4+1/x-1/x^2]-1+1/x]" is incomplete; more input is needed.
Syntax::sntxi: Incomplete expression; more input is needed.