You can give both plots the same PlotRange -> {{0, 2}, {0, 4}}
:
Plot[x, {x, 0, 1},
Epilog -> {Text[Style["y=" <> ToString[1], 10], {0.1, 0.1}]},
PlotRange -> {{0, 2}, {0, 4}}]
Plot[2 x, {x, 0, 2},
Epilog -> {Text[Style["y=" <> ToString[2], 10], {0.4, 0.8}]},
PlotRange -> {{0, 2}, {0, 4}}]
Overlay[{%%, %}]
Instead of Overlay
, you may want to experiment with a single Plot
for both functions:
Plot[{x, 2 x}, {x, 0, 2},
Epilog -> {Text[Style["y=" <> ToString[1], 10], {0.1, 0.1}],
Text[Style["y=" <> ToString[2], 10], {0.4, 0.8}]}]