I have:
f[x_] = 5 - 4/25*x^2.2;
Plot[{f[x], f[1] + (f[4] - f[1])/(4 - 1)*(x - 1),
f[1] + f'[1] (x - 1)}, {x, 0, 4.5},
PlotRange -> {{0, 6}, {0, 6}},
PlotLegends -> {"f", "secant", "tangent"},
Epilog -> {
Red, PointSize[Large], Point[{{1, f[1]}, {4, f[4]}}],
Black, Line[{{1, f[1]}, {4, f[1]}, {4, f[4]}}],
Text[Style["f", Black, Background -> White], {4.5, f[4.5]}],
Text[Style["(x,f(x))", Black, Background -> White], {1,
f[1]}, {1.2, 1.2}],
Text[Style["(x+Δx,f(x+Δx))", Black,
Background -> White], {4, f[4]}, {1.2, 1.2}],
Text[Style["dx=Δx", Black,
Background -> White], {2.5, f[1]}, {0, -1.2}],
},
AxesLabel -> {"x", "y"}, AxesStyle -> Arrowheads[{0, 0.03}]
]
Now I'd like to add the distance labels dy and $\Delta x$ on the right-hand side. What's the best way to draw an arrow with arrow heads and each end and a little horizontal line above and below the arrowhead tip? I know I can do it with Graphics, but just wondering if there is already an arrowhead style that might do this.