Edit and compile if you like:
% Author: Izaak Neutelings (June, 2017)% based on code from a friend\documentclass[border=3pt,tikz]{standalone}\usepackage{amsmath} % for \dfrac\usepackage{tikz}\tikzset{>=latex} % for LaTeX arrow head\usepackage{pgfplots} % for the axis environment\begin{document}% DRAW PLOT: sin, cos, tan\begin{tikzpicture}[domain=-pi:pi,xscale=2/pi]%https://tex.stackexchange.com/questions/45151/format-numbers-as-a-fraction-of-pi-with-tikz-pgfmathprintnumber% limits\def\xa{ -pi-0.3}\def\xb{3*pi+0.4}\def\ya{-3.4}\def\yb{ 3.6}\def\N{100} % number of points% axes & grid\draw[xstep=pi/2,very thin, color=gray](\xa,\ya) grid (\xb,\yb);\draw[->](\xa,0) -- (\xb,0)node[right] {$x$};\draw[->](0,\ya) -- (0,\yb)node[left] {$y$};% ticks\draw[] % xnode[below,scale=0.9] at ( -pi, 0) {$-\pi$}node[below,scale=0.9] at ( -pi/2, 0) {$-\dfrac{\pi}{2}$}node[below,scale=0.9] at ( 0, 0) {0}node[below,scale=0.9] at ( pi/2, 0) {$\dfrac{\pi}{2}$}node[below,scale=0.9] at ( pi, 0) {$\pi$}
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Nice work your graphs of trigonometric function! I have just noticed that line 42 is a duplicate of line 39.