Graphics, Figures & Tables ⇒ Plot problem

[gamename]

Hi,please help me, I have to make this plot with tikz
by tommorow and i am new at learning latex so I don't know how to do it
the function is ax^2-3x+cos(90x) where a={-2.4,-2.1,...,2.4}
it needs to be done with \addplot{} and \foreach{}
xmin=-5,xmax=5,ymin=-20 ymax=20
I would be really thankful

[Johannes_B]

This seems to be a crosspost and a homework question.