1. Решить методом подстановки:

{2x+3y=27

{x-y=11

{3a+4b=253

{5a-b=0

{6x-5y=43

{4x+3y=73

{5x+10y=54

{10x+5y=46,5

{12x-7y=2

{9x+14y=7

{2x+3y=27

{x-y=11

{2x+3y=27

{x-11 = y

{2x+3 (х-11) = 27

{x-11 = y

{5x=60 х=12; у=12-11=1

{x-11 = y

х=12

у=1

{3a+4b=253 {3a+4b=253 {3a+4*5a=253 {23a=253 a=11

{5a-b=0 {b=5a {b=5a {b=5a b=55

ответ: a=11

b=55

{6x-5y=43 {x = (43+5y) / 6 {x = (43+5y) / 6 {x = (43+5y) / 6

{4x+3y=73 {4 * (43+5y) / 6+3y=73 { (86+10y) + 9y=219 {19y=133

{x = (43+5y) / 6 {x = (43+35) / 6=78/6=13

{y=7 {y=7

ответ: x=13

y=7

{5x+10y=54 {x = (54-10y) / 5 {x=10.8-2y {x=10.8-2y

{10x+5y=46,5 {10x+5y=46,5 {10 (10.8-2y) + 5y=46,5 {108 + (-20+5) y=46,5

{x=10.8-2y {x=10.8-2y {x=10.8-8.2=2.6

{15y=61.5 {y=4.1 {y=4.1

ответ: x=2.6

y=4.1

{12x-7y=2 {7y=12x-2 {y = (12x-2) / 7 {y = (12x-2) / 7

{9x+14y=7 {9x+14y=7 {9x+14 * (12x-2) / 7=7 {9x+24x-4=7

{y = (12x-2) / 7 {y = (12x-2) / 7 {y = (12/3-2) / 7 {y = (4-2) / 7 {y=2/7

{33x=11 {x=1/3 {x=1/3 {x=1/3 {x=1/3

ответ: x=1/3

y=2/7