I created it with the following Gnuplot code:

1. set the output

set terminal svg enhanced fname "Times" fsize 18 set output "trigonometric_functions.svg"

1. axis properties

set xrange [-1.5*pi:1.5*pi] set yrange [-3:3] set grid xtics ytics set key 7,3

plot sin(x) title "sine" with lines linewidth 2,\

    cos(x) title "cosine" with lines linewidth 2,\
    tan(x) title "tangent" with lines linewidth 2,\
    1/cos(x) title "secant" with lines linewidth 2,\
    1/sin(x) title "cosecant" with lines linewidth 2,\
    1/tan(x) title "cotangent" with lines linewidth 2

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