1.
{ 2х/3 - 3/4 > x/2 + 5/3,
{ 7x - 3 > 4х + 2,
{ 8х/12 - 9/12 > 6x/12 + 20/12,
{ 7x - 3 > 4х + 2,
{ 8х - 6х > 20 + 9
{ 7x - 4х > 3 + 2,
{ 2х > 29,
{ 3х > 5,
{ х > 14,5,
{ х > 1 2/3,
2.
{ 7х - 5у = 13,
{ 4х - 3у = 7,
из 1 ур-ия:
х = (13 + 5у) / 7,
подставим во 2 ур-ие:
4 * ((13 + 5у) / 7) - 3у = 7,
52/7 + 20у/7 - 3у = 7,
52/7 + 20у/7 - 21у/7 = 49/7,
у = 3,
х = (13 + 5у) / 7 = (13 + 5*3) / 7 = 4,
3.
х³ - 2х² - х + 2 = 0,
(х³ - 2х²) - (х - 2) = 0,
х²* (х - 2) - (х - 2) = 0,
(х - 2)(х² - 1) = 0,
(х - 2)(х - 1)(х + 1) = 0,
х - 2 = 0, х - 1 = 0, х + 1 = 0,
х1 = 2, х2 = 1, х3 = -1