84,87,88,89,90

ա) Գ-x

Մ-y

{x=y-5

{x+y=61

y-5+y=61

2y=66

y=66/2=33

x=33-5=28

բ) Հ-x

Ա-y

{x=y+18

{x+y=66

y+18+y=66

2y=66-18=48

y=48/2=24

x=24+18=42

I ճ-x

II ճ-y

{x=y-7

{x+y=41

y-7+y=41

2y=34

y=34/2=17

x=17-7=10

Լայնություն -x
Երկարություն -y

{x=y+4

{2(x+y)=52

2x+2y=52

2(y+4)+2y=52

2y+8+2y=52

4y=52-8=44

y=44/4=11սմ

x=11+4=15սմ

{x+y=30

{100x+150y=3500

x=30-y

100(30-y)+150y=3500

3000-100y+150y=3500

-100y+150y=3500-3000

50y=500

y=500/50=10

x=30-10=20

բ-x

ս-y

{4x+2y=36000

{2x+3y=22000

2x+y=18000

y=18000-2x

2x+3(18000-2x)=22000

2x+54000-6x=22000

-4x= -32000

x= -32000/-4=8000

y=18000-2*8000=2000