1·If you want to get the unknown number, you should know the known number first.
如果要想求出未知数,你首先得知道已知数。
2·In math, X is used to stand for an unknown number.
在数学中,X被用来代表一个未知数。
3·Write out the equality that contains unknown number.
列出含有未知数的等式。
4·The sign X stands for an unknown number.
在代数中,符号x通常代表一未知数。