Spacing under square root

How can I remove space automatically added above expression under square root when I write for example\sqrt{k^2_t-k^2}. In fraction\frac{\sqrt{k^2_t-k^2}}{1} there isn't this type of space.

• Welcome to TeX.SE. It depends on where you are writing the first square root. if you type $\sqrt{k^2_t-k^2}$ you'll get the root with no additional space, since expressions between $...$ (or $$...$$) are in-line mode. Otherwise if you type $\sqrt{k^2_t-k^2}$ you'll get the root with space, because it is displaystyle mode. – Cragfelt Jan 14 '18 at 23:39
• You can remove it by using \textstyle prior to \sqrt, note however that this affacts more than just that space. – Skillmon Jan 14 '18 at 23:53

When TeX is in display-math mode, the numerator and denominator of a fraction are rendered in text style. If you want to apply text style to other material in a display-math environment, you need to provide the directive \textstyle explicitly.
\documentclass{article}
$% start an unnumbered display math group \sqrt{k^2_t-k^2} \qquad {\textstyle\sqrt{k^2_t-k^2}} \qquad \frac{\sqrt{k^2_t-k^2}}{1}$