daca a-2b=7 atunci calculați x din următoarele relații: a) x+3a-6b=30​

Răspuns:

a-2b=7

x+3a-6b=30

x+3(a-2b)=30

x+3·7=30

x=30-21=>x=9

_______

x-24+5a-10b=69

x-24+5(a-2b)=69

x-24+5·7=69

x-24+35=69

x=69+24-35=>x=58

_____

7a-x-14b=9

7a-14b-x=9

7(a-2b)-x=9

7·7-x=9

49-x=9

x=49-9=>x=40

_______

x+20+2a=4b+74

x+2a-4b=74-20

x+2(a-2b)=54

x+2·7=54

x+14=54=>x=54-14=>x=40

dam factor comun si folosim proprietatile adunarii si scaderii in principiu comutativitatea

a - 2b = 7 <=> a = 2b + 7

a) [tex]\it x + 3a - 6b = 30 <=> x + 3(2b + 7) - 6b = 30 <=> x + 6b + 21 - 6b = 30 <=> x + 21 = 30 <=> x = 30 - 21 <=> x = 9[/tex]

b) [tex]\it x - 24 + 5a - 10b = 69 <=> x - 24 + 5(2b + 7) - 10b = 69 <=> x - 24 + 10b + 35 - 10b = 69 <=> x + 11 = 69 <=> x = 69 - 11 <=> x = 58[/tex]

c) [tex]\it 7(2b + 7) - x - 14b = 9 <=> 14b + 49 - x - 14b = 9 <=> -x = 9 - 49 <=> -x = -40 <=> x = 40[/tex]

d) [tex]\it x + 20 + 2a = 4b + 74 <=> x + 20 + 2(2b + 7) = 4b + 74 <=> x + 20 + 4b + 14 = 4b + 74 <=> x + 4b - 4b = 74 - 20 - 14 <=> x = 40[/tex]