Срешением f(2x+1)=x^2-3x f(1-3x)=6x^2+2x

Если надо найти f(x):

1) 2x + 1 = t
x = (t-1)/2

f(t) = (t-1)²/4 - 3(t-1)/2 = t²/4 - t/2 - 1/4 - 3t/2 +3/2 = t²/4 -2t + 5/4

f(x) = (x² - 8x + 5)/4

2) 1 - 3x = t
x = (1-t)/3

f(t) = 2(1-t)²/3 + 2(1-t)/3 = 2(1-t)(2-t)/3 = (2t² - 6t + 4)/3

f(x) = (2x² - 6x + 4)/3