runge[x_] := 1 / (1 + 25 x^2)

data5 = Table[
{x, runge[x]},
{x, {-1, -1/2, 0, 1/2, 1}}
]

int5 = InterpolatingPolynomial[data5, x] // Expand

data7= Table[
{x, runge[x]},
{x, {-1, -2/3, -1/3, 0, 1/3, 2/3, 1}}
]

int7 = InterpolatingPolynomial[data7, x] // Expand

Show[
Plot[runge[x], {x, -1, +1}],
ListPlot[data5, PlotStyle -> Red],
Plot[int5, {x, -1, +1}, PlotStyle -> Red],
ListPlot[data7, PlotStyle -> Red],
Plot[int7, {x, -1, +1}, PlotStyle -> Red]
]