Răspuns:
Explicație pas cu pas:
7).
{3x+5y=27 I·(-2) =>
{6x+4y=40
{-6x-10y = -54
{6x+4y = 40 =>
--------------------
-6y = -14 => y = 14/6 = 7/3
x = ³⁾27-5·7/3 = (81-35)/3 = 46/3
x = 46/3 ; y = 7/3
8).
{5x+7y=16 I·5
{7x-5y=9 I·7 =>
{25x+35y = 80
{49x-35y = 63 =>
74x = 143 => x = 143/74
y = (7x-9)/5 = (1001/74 - ⁷⁴⁾9)/5
y = (1001-666)/(74·5) = 67/74
x = 143/74 ; y = 67/74
9).
{2(4x+5) = 5(3y - 4)
{2(x-6) = 3(1-y) <=>
{8x+10 = 15y -20
{2x-12 = 3-3y <=>
{8x-15y = -30
{2x+3y = 15 I·4 =>
{8x-15y = -30
{-8x-12y = 60
--------------------
-27y = 30 => y = -30/27 = > y = -10/9
x = (15-3y)/2 = (15 + 10/3) /2 => x = 55/6
x = 55/6 ; y = -10/9
