Plotting a function not working correctly

[Ollie]

Hey!
I've been experimenting and finding roots of polynomials graphically but today I came across a weird glitch.
I tried to plot the following function: 0.1x^5 + 1.3x^4 - x^3 - 15x^2 - 8x - 1, a function that has 5 different roots.
The problem is that I cannot see the line that is supposed to cross the x-axis for the first time, all I see are very sparsely scattered dots instead of a continuous line.
Has anyone else come across such a problem before on the Prime? If so, have you found a fix for it?