ankhi wrote:Code: Select all
\begin{equation} D_{12} \propto {\bigg({(m_1 m_2)\frac(m_1+m_2 )}\bigg)^{-1\frac{2}}} \end{equation}
\frac
is a command that needs two arguments which for LaTeX and this case should mean: it must be followed by two pairs of balanced braces that contain numerator and denominator:
Code: Select all
\frac{numerator}{denominator}
BTW: Did you read some resources like the Not So Short Introduction to LaTeX?