# How to define the plot area to the inside of a circle

I dont want the lines not to go beyond the inside of the shown circle but i dont really know how to do it.

PlotRange -> {{-1, 1}, {-1, 1}} only sets a rectangular area.

Plot[{{1.2 (-1 + x), -0.9 - 0.5 (-0.18 + x), -0.35 + 2.8 (0.9 x)},
Sqrt[(1 - x^2)],  -Sqrt[(1 - x^2)]}, {x, -1, 1},
PlotStyle -> {Blue},  PlotRange -> {{-1, 1}, {-1, 1}},
ImageSize -> Large]

• Also related to RegionFunction: (32219) and (50767) – MarcoB Jun 3 '15 at 16:10

Use the option RegionFunction:

Plot[{{1.2 (-1 + x), -0.9 - 0.5 (-0.18 + x), -0.35 + 2.8 (0.9 x)},
Sqrt[(1 - x^2)], -Sqrt[(1 - x^2)]}, {x, -1, 1}, PlotStyle -> {Blue},
PlotRange -> {{-1, 1}, {-1, 1}}, ImageSize -> Large,
RegionFunction -> Function[{x, y}, -Sqrt[(1 - x^2)] <= y <= Sqrt[(1 - x^2)]]]


Or use ConditionalExpression to restrict the first three functions to the appropriate region:

Plot[{ConditionalExpression[1.2 (-1 + x),
-Sqrt[(1 - x^2)] <= 1.2 (-1 + x) <= Sqrt[(1 - x^2)]],
ConditionalExpression[-0.9 - 0.5 (-0.18 + x),
-Sqrt[(1 - x^2)] <= -0.9 - 0.5 (-0.18 + x) <=  Sqrt[(1 - x^2)]],
ConditionalExpression[-0.35 + 2.8 (0.9 x),
-Sqrt[(1 - x^2)] <= -0.35 + 2.8 (0.9 x) <=  Sqrt[(1 - x^2)]],
Sqrt[(1 - x^2)], -Sqrt[(1 - x^2)]}, {x, -1, 1},
PlotStyle -> {Blue}, PlotRange -> {{-1, 1}, {-1, 1}},
ImageSize -> Large]
(* same picture *)