Х+у = 4
у=х-4
х^2+3(х-4)=-9
х^2+3х-12+9=0
д=9 -4*(-3)=21
х1=-2
х2=5
1) 15 ^ 6 = ( 3^6 )•( 5^6 )
2) ( 3^6 ) : ( 3^5 ) = 3
3) ( 5^6 ) : ( 5^4 ) = 5^2 = 25
4) 3 • 25 = 75
Ответ 75
{х-4у=7
{2х-у=7
{х=7=4у
{2х-у=7
2(7=4у)-у=7
х=3
(х,у)=(3,-1)
{3-4 *(-1)=7
{2*3-9-1)=7
{7=7
{7=7