# How do I fix error “I do not know the key '/tikz/show background rectangle'”

I don't know why, but I keep getting issues using the tkz-euclide package. Here are several problems:

Problem 1:

\documentclass[svgnames]{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usepackage{xcolor}
\usepackage{tkz-fct}
\usetkzobj{all}

\begin{document}
\tikzset{background rectangle/.style={fill=black}}
\begin{tikzpicture}[show background rectangle]
\tkzInit[ymin=-1.5,ymax=7,xmin=-1,xmax=+11]
\tkzClip
\tkzDefPoint(0,0){O}
\tkzDefPoint(1,0){I}
\tkzDefPoint(10,0){A}
\tkzDefPointWith[orthogonal](I,A) \tkzGetPoint{H}
\tkzDefMidPoint(O,A) \tkzGetPoint{M}
\tkzInterLC(I,H)(M,A)\tkzGetPoints{C}{B}
\tkzDrawSegments[color=white,line width=1pt](I,H O,A)
\tkzDrawPoints[color=white](O,I,A,B,M)
\tkzMarkRightAngle[color=white,line width=1pt](A,I,B)
\tkzDrawArc[color=white,line width=1pt,style=dashed](M,A)(O)
\tkzLabelSegment[white,right=1ex,pos=.5](I,B){$\sqrt{a}$}
\tkzLabelSegment[white,below=1ex,pos=.5](O,I){$1$}
\tkzLabelSegment[pos=.6,white,below=1ex](I,A){$a$}
\end{tikzpicture}
\end{document}


Output:

! Package pgfkeys Error: I do not know the key '/tikz/show background rectangle
' and I am going to ignore it. Perhaps you misspelled it.

See the pgfkeys package documentation for explanation.
Type  H <return>  for immediate help.
...

l.11 ...in{tikzpicture}[show background rectangle]

?

Process has been terminated ...


What it's supposed to look like:

I also have one more question:

How do I install tkz-fct(for drawing graphs and functions), how to use it, and which articles I can use?

• If you use MikTeX, there is a package manager to install new packages. – Sigur Oct 20 '18 at 18:36
• In order to use show background rectangle, you need to say \usetikzlibrary{backgrounds}. – user121799 Oct 20 '18 at 19:25
• I took the liberty of making the title more descriptive, hope you don't mind. – Torbjørn T. Oct 20 '18 at 21:16
• Thank you for making the title more descriptive! It does actually make it easier to understand! – CuriousEinstein Oct 20 '18 at 23:01

Once I add \usetikzlibrary{backgrounds}, there is no error.

\documentclass[svgnames]{article}
\usepackage{tikz}
\usepackage{tkz-euclide}
\usepackage{xcolor}
\usepackage{tkz-fct}
\usetkzobj{all}
\usetikzlibrary{backgrounds}
\begin{document}
\tikzset{background rectangle/.style={fill=black}}
\begin{tikzpicture}[show background rectangle]
\tkzInit[ymin=-1.5,ymax=7,xmin=-1,xmax=+11]
\tkzClip
\tkzDefPoint(0,0){O}
\tkzDefPoint(1,0){I}
\tkzDefPoint(10,0){A}
\tkzDefPointWith[orthogonal](I,A) \tkzGetPoint{H}
\tkzDefMidPoint(O,A) \tkzGetPoint{M}
\tkzInterLC(I,H)(M,A)\tkzGetPoints{C}{B}
\tkzDrawSegments[color=white,line width=1pt](I,H O,A)
\tkzDrawPoints[color=white](O,I,A,B,M)
\tkzMarkRightAngle[color=white,line width=1pt](A,I,B)
\tkzDrawArc[color=white,line width=1pt,style=dashed](M,A)(O)
\tkzLabelSegment[white,right=1ex,pos=.5](I,B){$\sqrt{a}$}
\tkzLabelSegment[white,below=1ex,pos=.5](O,I){$1$}
\tkzLabelSegment[pos=.6,white,below=1ex](I,A){$a$}
\end{tikzpicture}
\end{document}


• Thank you for mentioning the \usetikzlibrary{backgrounds}! – CuriousEinstein Jan 30 '19 at 1:04