Hallo Schiestel,
R(x) = 10x − 0.02x2 (in Euro)
a)
10x − 0.02x2 = 800 ⇔ 0.02 x2 - 10 x + 800 = 0
⇔ x2 - 500·x + 40000 = 0
x2 + px + q = 0
pq-Formel: p = - 500 ; q = 40000
x1,2 = - p/2 ± \(\sqrt{(p/2)^2 - q}\)
→ x1 = 400 ; x2 = 100 [ € ]
b)
R'(x) = 10 - 0.04x → R'(15) = 9,4 [ €/ME ]
Gruß Wolfgang