\input{preamble-standalone.ltx}
\begin{document}

% Ex. No. 243 (Section 31.1.1 : Example 1: change line width)

\begin{tikzpicture}
   \tkzSetUpLine[color=blue,line width=1pt]
\begin{scope}[rotate=-90]
    \tkzDefPoint(10,6){C}
    \tkzDefPoint( 0,6){A}
    \tkzDefPoint(10,0){B}
    \tkzDefPointBy[projection = onto B--A](C)
    \tkzGetPoint{H}
    \tkzDrawPolygon(A,B,C)
    \tkzMarkRightAngle[size=.4,fill=blue!20](B,C,A)
    \tkzMarkRightAngle[size=.4,fill=red!20](B,H,C)
    \tkzDrawSegment[color=red](C,H)
\end{scope}
 \tkzLabelSegment[below](C,B){$a$}
 \tkzLabelSegment[right](A,C){$b$}
 \tkzLabelSegment[left](A,B){$c$}
 \tkzLabelSegment[color=red](C,H){$h$}
 \tkzDrawPoints(A,B,C)
 \tkzLabelPoints[above left](H)
 \tkzLabelPoints(B,C)
 \tkzLabelPoints[above](A)
\end{tikzpicture}

\end{document}