Given supply and demand functions
p1(x) = −0.1x2 − x + 44 (demand)
p2(x) = 0.1x2 + 2x + 24 (supply)
At equilibrium, demand equals supply, hence
p1(x)=p2(x) =>
-0.1x^2-x+44 = 0.1x^2+2x+24
rearrange
0.2x^2+3x-20=0 => x^2+15x-100
Solve for x using the quadratic formula:
x=(-15 ± sqrt(625))/2=-7.5 ± 12.5
reject negative root to give x=5