Plot Taylor expansion of polynomial

Question

I have a polynomial:

f[x_] := x^3 + 2*x^2 + 4

and I create a function that implements the Taylor expansion:

ft[x_, x0, n] := Normal[Series[f[x], {x, x0, n}]] 

If I implement the expansion, the output is as expected:

ft[x, 5, 2]

(179 + 95 (-5 + x) + 17 (-5 + x)^2)

If I then plot the output, it works as expected:

Plot[179 + 95 (-5 + x) + 17 (-5 + x)^2, {x, -10, 10}]

But if I do it in one step, I obtain an error:

Plot[{f[x], ft[x, 5, 2]}, {x, 0, 10}]

(General::stop: Further output of General::ivar will be suppressed during this calculation.)

• Why causes this error?
• How I can solve it keeping the one step approach? I know there are examples such as this one, but they use multiple steps.

Answer 1

f[x_] := x^3 + 2*x^2 + 4
ft[x_, x0_, n_] := Normal[Series[f[x], {x, x0, n}]]

ft[x, 5, 2]

179 + 95 (-5 + x) + 17 (-5 + x)^2

Plot[{f[x], Evaluate@ft[x, 5, 2]}, {x, 0, 10}]