Draw an isosceles right triangle. Label the angle measures and use tick marks to indicate congruent sides.

\begin{tikzpicture}

\draw (0,0) -- (2,0) -- (1,2) -- cycle;
\draw (0,0) -- (1,2);
\draw (2,0) -- (1,2);
\draw (1,0) node[below] {90$^\circ$};
\draw (2,0) node[below] {45$^\circ$};
\draw (1,2) node[above] {45$^\circ$};
\draw (0.5,1) node[left] {$\cong$};
\draw (1.5,1) node[right] {$\cong$};
\end{tikzpicture}