S = 2648000 руб
k = 1 + a/100
a = 10
S₁ = Sk - x
S₂ = S₁k - x = (Sk - x)k - x) = Sk² - kx - x
S₃ = S₂k - x = (Sk² - kx - x)k - x) = Sk³ - k²x - kx - x
Sk³ - k²x - kx - x = 0
2648000 * 1.1³ - 1.1²x - 1.1x - x = 0
3524488 - 1.21x - 1.1x - x = 0
1.21x + 1.1x + x = 3524488
3.31x = 3524488
x = 1064800 руб
S=a*b:2
или
S=a*b*1/2
S=14*20:2=140мм2=14см2
решениееееее................