Just sticking the text straight in the maths environment wont give you the results you want. U_2 Second element of the sequence u_n. Mathematical expressions that are given in a line are known as expressions.
An operator is a function that is written as a word.
In this video we drive how to type math equations in latex. If you enter ym xthen LaTeX ignores the space and in the output the m is next to the x. The second one is used to write expressions that are not part of a text or paragraph and are therefore put on separate lines. U_2 textrmSecond element of the sequence u_n u_2 textrmSecond element of the sequence u_n Do not forget the space before closing.