c= 2017
a + b + 2017 = 2018
a - b +  2017  = 2019.

...........
f(2 ) = 4 a + 2 b + 2017 

Cách làm bài 4 b giống 4 a là bỏ trị tuyệt đối , bạn có 2 số

đáp số bài 4 b 
x = 3/20 hay x = - 7/20

\(\dfrac{2x}{3}\) = \(\dfrac{3y}{4}\) = \(\dfrac{4z}{5}\) và x + y + z = 4

\(\dfrac{12x}{18}\) = \(\dfrac{12y}{16}\) = \(\dfrac{12y}{15}\)= \(\dfrac{12x+12y+12z}{18+16+15}\)= \(\dfrac{12\left(x+y+z\right)}{49}\)= \(\dfrac{12.4}{49}\) =\(\dfrac{48}{49}\)

x = \(\dfrac{48}{49}\): \(\dfrac{12}{18}\)= \(\dfrac{72}{49}\), y = \(\dfrac{48}{49}\): \(\dfrac{12}{16}\) = \(\dfrac{64}{49}\), z = \(\dfrac{48}{49}\): \(\dfrac{12}{15}\) = \(\dfrac{60}{49}\)

1\(\dfrac{2}{3}\): x = - \(\dfrac{4}{3}\)

\(\dfrac{5}{3}\): X = \(\dfrac{-4}{3}\)

X =          \(\dfrac{5}{3}\)   : \(\dfrac{-4}{3}\) 

X = \(\dfrac{5}{3}\) . \(\dfrac{-3}{4}\)

X = \(\dfrac{-5}{4}\)

-\(\dfrac{2}{7}\) . X = \(\dfrac{-1}{4}\)

X = \(\dfrac{-1}{4}\) : \(\dfrac{-2}{7}\)

X = \(\dfrac{1}{4}\) . \(\dfrac{7}{2}\)

X =  \(\dfrac{7}{8}\)

- \(\dfrac{2}{7}\).X = - \(\dfrac{-1}{4}\)

X = \(\dfrac{-1}{4}\) : \(\dfrac{-2}{7}\)

X = \(\dfrac{1}{4}\) . \(\dfrac{7}{2}\)

X = \(\dfrac{7}{8}\)

x - 1\(\dfrac{1}{3}\) = 2

X - \(\dfrac{4}{3}\) = 2

X = 2 + \(\dfrac{4}{3}\)

X = \(\dfrac{10}{3}\)

\(x-1\dfrac{1}{3}=2\)

  \(x-\dfrac{4}{3}=2\)

          \(x=2+\dfrac{4}{3}\)

          \(x=\dfrac{10}{3}\)

x + 1,5 = \(\dfrac{5}{3}\)

x   = \(\dfrac{5}{3}\) -  1,5

x = \(\dfrac{5}{3}\) - \(\dfrac{3}{2}\)

x = \(\dfrac{10}{6}\) - \(\dfrac{9}{6}\)

x = \(\dfrac{1}{6}\)

\(x+1,5=\dfrac{5}{3}\)

  \(x+\dfrac{3}{2}=\dfrac{5}{3}\)

          \(x=\dfrac{5}{3}-\dfrac{3}{2}\)

          \(x=\dfrac{1}{6}\)